Here are the latest updates:
Update 2:55 a.m. EDT April 26: Sri Lanka police said on Twitter that Mohamed Zahran, the leader of local militant group National Towheed, died in one of the nine suicide bombings Easter Sunday, The Associated Press reported. Police said they also arrested the group's second-in-command.
Security measures in Colombo were beefed up Friday as authorities warned of another possible attack, according to the AP. Police asked people of all faiths to pray privately Friday, CNN reported.
Update 1:54 a.m. EDT April 26: Authorities in Sri Lanka said Friday the suspected leader of the attacks on Easter Sunday died in the Shangri-La hotel bombing, according to The Associated Press.
Update 6 p.m. EDT April 25: Sri Lanka lowered the death toll from the Easter suicide bombings by nearly one-third, to 253, as authorities hunted urgently for a least five more suspects and braced for the possibility of more attacks in the coming days.
In rolling back the number of dead from 359, a top Health Ministry official, Dr. Anil Jasinghe, said in a statement that the blasts had damaged some bodies beyond recognition, making accurate identification difficult.
Update 7:20 a.m. EDT April 24: Sri Lanka officials said 60 people have been arrested in connection with Sunday's bombings, according to The Associated Press.
A police spokesman said nine suicide bombers carried out the attacks, apparently contradicting government officials' previous statement that seven bombers were involved, the AP reported.
Ruwan Wijewardene, Sri Lanka's junior defense minister, described the attackers as educated people from upper- and middle-class households, the AP reported.
Although authorities previously said the terror group National Towheed Jamaar was behind the attacks, Wijewardene said Wednesday that the perpetrators had split off from that group and another one called JMI, the AP reported. He did not say what the acronym stands for.
Wijewardene also amended his earlier statement that the bombings were in retaliation for the deadly mass shootings at New Zealand mosques last month, saying Wednesday that the Christchurch attacks may have been a motivation but no evidence has confirmed the link, the AP reported.
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Update 11:30 p.m. EDT April 23: Police said the death toll in the Easter attacks has risen to 359 and more suspects have been arrested.
Police spokesman Ruwan Gunasekara also said Wednesday morning that 18 suspects were arrested overnight, raising the total detained to 58.
The prime minister warned on Tuesday that several suspects armed with explosives were still at large.
Update 1 p.m. EDT April 23: Sunday's bombings claimed the lives of 45 children, officials with the United Nation's Children's Fund said Tuesday in a statement.
“Many children have lost one or both parents, and countless children have witnessed shocking and senseless violence,” UNICEF officials said.
More than 320 people were killed and 500 injured in the bombings.
Update 7:11 a.m. EDT April 23: The Islamic State group has claimed responsibility for the deadly Easter Sunday attacks in Sri Lanka, the Guardian and the Washington Post are reporting.
The group, which has lost all the territory it once held in Iraq and Syria, has made a series of unsupported claims of responsibility.
Update 5:55 a.m. EDT April 23: Sri Lankan officials said the death toll from Sunday's bombings has risen to 321, the Guardian and the Washington Post reported Tuesday.
The news came as Sri Lankan Defense Minister Ruwan Wijewardene said the attacks were "carried out in retaliation" for the deadly mosque shootings in New Zealand last month, according to The Associated Press.
So far, at least 40 people have been arrested in connection with the attacks, authorities said.
Meanwhile, the country observed a day of mourning, including a three-minute moment of silence Tuesday morning. Mass burials also were held in Negombo, the Guardian reported.
Officials have declared a state of emergency in Sri Lanka, giving military officials "enhanced war-time powers," the AP reported.
Authorities also are facing criticism amid reports that a top police official sent a letter April 11 to four security agencies warning that terror group National Towheed Jamaar was planning suicide bombings at churches, the AP reported.
Update 9:45 p.m. EDT April 22: Ranil Wickremesinghe, the Prime Minister of Sri Lanka, issued a statement in response to the bombings.
“Today as a nation we mourn the senseless loss of innocent lives this past Easter Sunday. I would like to thank the military and police forces, the medical personnel and all those who have worked bravely and tirelessly without concern for their own safety, to ensure the safety and security of our citizens. It is imperative that we remain unified as Sri Lankans in the face of this unspeakable tragedy.”
A three-minute moment of silence for the victims of the explosions will be held at 8:30 a.m. local time, according to BBC reporter Azzam Ameen.
Update 8 p.m. EDT April 22: The two Australians who officials said had been killed in the explosions have been identified by a family member.
Sudesh Kolonne told Australian Broadcasting Corp. his wife, Manik Suriaaratchi, and their 1-year-old daughter Alexendria were killed in an attack in Negombo, which is north of Sri Lanka's capital Colombo.
Kolonne said he was outside when the explosion happened.
“I heard a huge noise and I jumped into the church and I saw that my wife and my daughter were on the floor,” he said. “I just saw my daughter on the floor and I tried to lift her up, (but) she was already dead. And (then) exactly the same… next my wife is there.”
Kolonne said he and his family moved from Melbourne to Sri Lanka in 2014 when his wife started a consultancy business.
“I don’t know what to do,” he said. “We used to go to that church every Sunday. We never expected this.”
Update 4:50 p.m. EDT April 22: A spokeswoman for the Federal Bureau of Investigation confirmed to The AP that the agency is providing assistance with the investigation into the bombings. She would not provide specifics.
Update 3:50 p.m. EDT April 22: In an email to parents, officials at Sidwell Friends, a private school in the Washington-area, confirmed one of their students was killed in Sunday's bombings, The Washington Post reported.
School officials identified the student as Kieran Shafritz de Zoysa, a fifth-grade boy who had been on leave in Sri Lanka for the last year, according to the Post.
“Kieran was passionate about learning, he adored his friends, and he was incredibly excited about returning to Sidwell Friends this coming school year,” school officials said in the letter. “We are beyond sorry not to get the opportunity to welcome Kieran to the Middle School.”
State Department officials said earlier Monday that at least four Americans were among the nearly 300 people killed in Sunday’s attacks. Officials with the English education management company Pearson confirmed that one of the company’s Denver-based employees had also been killed in the bombings.
Update 3 p.m. EDT April 22: Officials with the U.S. State Department confirmed Monday that at least four Americans were among the nearly 300 people killed in Sunday's bombings in Sri Lanka.
The department said that in addition to those killed, several others were seriously injured. Officials gave no details about the identities of the victims, citing privacy concerns.
Earlier Monday, officials with the English education management company Pearson confirmed that one of the company’s Denver-based employees had been killed in the bombings. Pearson CEO John Fallon said Dieter Kowalski died shortly after arriving at his hotel in Sri Lanka for a business trip.
Update 2:10 p.m. EDT April 22: President Donald Trump said he spoke Monday to Sri Lankan Prime Minister Ranil Wickremesinghe after a series of bomb attacks in the country.
In a tweet, Trump said he told Wickremesinghe “the United States stands by him and his country in the fight against terrorism.”
“(I) also expressed condolences on behalf of myself and the People of the United States,” Trump wrote.
Earlier Monday, U.S. Secretary of State Mike Pompeo vowed the government would provide “all possible assistance” to help in the investigation.
Update 1:50 p.m. EDT April 22: Sri Lankan President Maithrpala Sirisena declared April 23 a national day of mourning in a statement obtained Monday by The Associated Press.
In the statement, Sirisena said he planned to meet with foreign diplomats to seek international assistance. U.S. Secretary of State Mike Pompeo said earlier Monday that the U.S. would provide “all possible assistance” to help in the investigation.
Officials said nearly 40 foreign tourists from 11 countries were killed in Sunday’s attacks on churches and hotels in Sri Lanka.
Update 11:20 a.m. EDT April 22: U.S. Secretary of State Mike Pompeo on Monday mourned the victims of Sunday's bomb attacks in Sri Lanka and promised the government would provide "all possible assistance" to Americans and Sri Lankans alike.
“We urge that any evil-doers be brought to justice expeditiously and America is prepared to support that,” he Pompeo said. “We also stand with the millions of Sri Lankas who support the freedom of their fellow citizens to worship as they please.”
Pompeo confirmed that Americans were among those killed in Sunday’s attack, though he didn’t specify the number of American victims.
“It’s heartbreaking that a country which has strived so hard for peace in recent years has been targeted by these terrorists,” he said.
Related: Sri Lanka attack: Danish billionaire loses three of his four children in bombings
Update 9:50 am. EDT April 22: A Denver man has been identified as one of the nearly 300 people killed Sunday in bombings in Sri Lanka, his employer confirmed Monday.
Dieter Kowalski worked as senior leader of the operation technical services team for Pearson, an education management company. Though the company is based in England, Kowalski worked in Pearson's Denver office, the Milwaukee Journal-Sentinel reported.
“Colleagues who knew Dieter well talk about how much fun he was to be around, how big-hearted and full-spirited he was,” Pearson CEO John Fallon said in a statement shared with company employees and posted Monday on LinkedIn. “They tell of a man to whom we could give our ugliest and most challenging of engineering problems, knowing full well that he would jump straight in and help us figure it out. Dieter, they tell me, was never happier than cheer-leading for our customers and our company and inspiring people in the best way he knew how – by helping them to fix things and doing it with joy, happiness and grace.”
Fallon said Kowalski died shortly after arriving at his hotel Sunday for a business trip.
Update 7:55 a.m. EDT April 22: Three children of Anders Holch Povlsen, who owns Bestseller clothing, were killed in Sunday's attacks, The Associated Press is reporting.
The 46-year-old Danish billionaire, who is also the largest shareholder in ASOS, and his family were on vacation in Sri Lanka, the AP reported.
Authorities said 39 foreigners were among the 290 people killed in Sunday’s attacks.
Meanwhile, a vehicle parked near St. Anthony's Shrine, one of the churches that was bombed Sunday, exploded Monday as police tried to defuse three bombs inside, according to the AP. At least 87 bomb detonators have been found in Colombo, officials said.
Police have detained at least 24 suspects in connection with Sunday’s bombings.
Update 5:15 a.m. EDT April 22: Government officials said the National Thowheed, a Sri Lankan militant group, was responsible for Sunday's deadly attacks, the Guardian is reporting. However, a government spokesman said an "international network" helped the attackers.
Seven suicide bombers caused six of the nine explosions Sunday, a forensic analyst told The Associated Press.
Authorities also said a second Chinese citizen and two Australian citizens were among those killed in Sunday's attacks. So far, the dead include citizens of the United States, India, Britain, China, Australia, Japan and Portugal, the AP reported.
Meanwhile, a Sri Lanka military official said crews defused a homemade pipe bomb discovered late Sunday on a road to the airport outside Colombo, the AP reported.
Update 12:10 a.m. EDT April 22: The death toll in the bombings has increased to 290 and more than 500 people have been wounded, according to police spokesman Ruwan Gunasekara. Among those killed are five Indians, who were identified in tweets from India's external affairs minister Sushma Swaraj and the Indian High Commission in Sri Lanka, The AP reported.
China and Portugal also said they lost citizens, and the U.S. said “several” Americans were also killed in the bombings.
The AP reported Sri Lankan officials said they would examine reports that intelligence failed to heed or detect warnings of a possible suicide attack.
"Some intelligence officers were aware of this incidence," Telecommunications Minister Harin Fernando said in a tweet, according to The AP. "Therefore there was a delay in action. Serious action needs to be taken as to why this warning was ignored."
Update 9:50 p.m. EDT April 21: Japan has confirmed at least one citizen death and four injuries from the bombings. The country has issued a safety warning to Japanese people in the country, telling them to avoid mosques, churches and public places like clubs, malls and government offices, The AP reported.
Foreign Minister Taro Kono expressed solidarity with Sri Lanka and sent his condolences to victims of the explosions. He also said Japan was committed to “combating terrorism.”
Update 5:40 p.m. EDT April 21: The Associated Press reported that, according to internet censorship monitoring group NetBlocks, social media has been blocked across the country after the attacks.
Most services, including YouTube, WhatsApp, Instagram, Snapchat and Facebook have been temporarily blacked out to curb false information spread, according to Sri Lankan officials. According to NetBlocks, such blackouts are usually ineffective.
Related: Sri Lanka explosions: Sri Lanka shuts down social media in wake of Easter attacks
"We are aware of the government's statement regarding the temporary blocking of social media platforms," Facebook, which owns Instagram and WhatsApp, said in a statement to The AP. "People rely on our services to communicate with their loved ones and we are committed to maintaining our services and helping the community and the country during this tragic time."
Update 3:28 p.m. EDT April 21: Police have 13 suspects in custody, impounded a vehicle they believed was used by suspects and located a safe house used by the attackers.
No one has claimed responsibility for what Sri Lankan officials have described as a terrorist attack by religious extremists.
Update 9:28 a.m. EDT April 21: Police have so far arrested three people in connection to the blasts, The Guardian reported. A motive for the bombings is still unclear, investigators said.
Update 8:46 a.m. EDT April 21: At least 207 people were killed and 450 hurt in Sunday's attacks, The Associated Press is reporting.
Officials said eight blasts targeted three churches, three hotels, a guesthouse and an area near a Dematagoda overpass, the AP reported.
Authorities reportedly have arrested seven people in connection with the incidents.
Update 8:07 a.m. EDT April 21: Sri Lankan officials say at least 190 people, including at least 27 foreigners and two police officers, were killed in Sunday's attacks, The Associated Press is reporting.
Seven people have been arrested in connection with the eight explosions, which rocked at least three churches and three hotels, as well as a guesthouse, officials said.
Update 7:35 a.m. EDT April 21: President Donald Trump tweeted condolences to the Sri Lankan people Sunday morning.
"The United States offers heartfelt condolences to the great people of Sri Lanka," Trump tweeted. "We stand ready to help!"
Update 7:19 a.m. EDT April 21: Hours after explosions at Sri Lankan churches and hotels left dozens dead and hundreds more injured, Pope Francis prayed for the victims during his annual Easter message at the Vatican.
Related: Sri Lanka explosions: Pope denounces attacks during Easter blessing
"I wish to express my heartfelt closeness to the Christian community (of Sri Lanka), wounded as it was gathered in prayer, and to all the victims of such cruel violence," Francis told the crowd in St. Peter's Square, according to Vatican News.
He later added: “I entrust to the Lord all those who have tragically perished, and I pray for the injured and all those who suffer as a result of this tragic event.”
Every year after leading Easter Mass, the pope delivers an “Urbi et Orbi” (“to the city and the world”) message, which addresses global issues and conflicts.
Update 5:32 a.m. EDT April 21: Two more blasts have been reported in Sri Lanka. A seventh explosion hit a hotel in Dehiwala, and an eighth blast was reported in the capital, Agence France-Presse is reporting.
Update 4:20 a.m. EDT April 21: At least 156 people were killed in blasts at three churches and three hotels in Sri Lanka, Agence France-Presse is reporting. The dead include 35 foreigners, officials said.
Update 3:34 a.m. EDT April 21: At least 137 people were killed in blasts at three churches and three hotels in Sri Lanka, Agence France-Presse is reporting. The dead include 45 people in Colombo, 67 in Negombo and 25 in Batticaloa, officials said. At least nine of the people killed were foreigners, the news agency reported.
More than 500 people were hurt in the explosions, according to The Associated Press.
Explosions hit three churches and three hotels in Sri Lanka on Easter Sunday, killing dozens of people and injuring nearly 300 more, news outlets are reporting.
According to The Associated Press, blasts occurred Sunday morning at St. Anthony's Shrine in Colombo, St. Sebastian's Church in Negombo and a church in Batticaloa. Explosions also rocked the Kingsbury, Cinnamon Grand and Shangri La hotels in Colombo, the BBC reported.
The Agence France-Presse news agency said 52 people died in the blasts. At least 283 people were taken to the hospital, the AP reported.
Suicide bombers may have caused at least two of the church blasts, a security official told the AP.
The Associated Press contributed to this report.