Passengers on two Atlanta-bound airliners got a scare Saturday when “credible” bomb threats sent via social media prompted the military to scramble fighter jets to escort the planes to Hartsfield-Jackson International Airport, but searches by a police bomb squad and the FBI turned up nothing threatening.

Airport spokesman Reese McCranie told The Atlanta Journal-Constitution at 3 p.m. that both flights — Delta 1156 from Portland, Ore., and Southwest 2492 from Milwaukee, Wisc. — had landed and were sitting on a taxiway waiting to be swept by the Atlanta police Bomb Squad.

“We believe the threats to be credible,” McCranie said, adding that Runway 27L was shut down while the threats were investigated. Authorities have not said what led them to give credence to the threats.

FBI spokesman Stephen Emmett told The Atlanta Journal-Constitution that NORAD scrambled military fighter jets to escort the two planes to Atlanta after the threats were made.

The FBI confirmed that the threats were made via Twitter. While authorities have not yet released information on the Twitter account responsible for the specific threatening tweets, someone calling himself “King Zortic” first posted messages to Delta on Twitter around noon that said, “I have a bomb on one of your planes, but I forgot which one when I left the airport. Can you help me find it?,” and “It was from Portland to Atlanta, I forgot the flight number, though. It was something like DL156 or DL 1556 I forgot the order.”

Another tweet read, “It was smuggled through one of the back entrances because the airport didn’t have much security around one of the entrances so the bomb is at the back of the plane. Everyone will know when it’s detonated.”

Messages later were sent to Southwest Airlines from the same Twitter account read, “A bomb was placed on SWA2492. It will be detonated at a random time of my choosing,” and “If anything happens to me I’ll make sure that more flights are targeted. I strongly suggest you don’t try anything stupid.”

By Sunday, that Twitter account had been suspended.

Passengers were taken off the Delta flight first, and at 4:45 p.m., passengers started exiting the Southwest plane. Bomb-sniffing dogs were seen checking the passengers and their carry-on bags as they deplaned and boarded buses.

At 5:35 p.m., Emmett said that the Delta plane and luggage had been cleared and released by the bomb squad, which was still examining the Southwest plane.

Britt Johnson, Special Agent In Charge of the Atlanta FBI Field Office, told Channel 2 Action News at 6 p.m. that both aircraft had been searched, and agents from the FBI and the Joint Terrorism Task Force were interviewing passengers.

Nothing suspicious was found on either aircraft.

“We haven’t found anything at this point,” Johnson said. “Nothing’s been found.”

Johnson said the FBI will “absolutely be doing everything we can to identify who made the initial threats and track them down.”

Toni Ellingen of San Diego, one of the passengers aboard the Southwest flight from Milwaukee, said she and her fellow passengers kept up with events using their smart phones and tablets. She had nothing but praise for the Southwest flight crew and Atlanta authorities.

“They handled it really well. Nobody panicked. The police handled it very well,” she said. “There wasn’t much they could do except check out the situation. Everybody was happy because we didn’t blow up.”

Ellingen was on her way back to San Diego after visiting family in Wisconsin. Southwest gave passengers stranded in Atlanta vouchers for a hotel, food and $100 off their next flight, Ellingen said.

She said the threat seemed a lot less serious once passengers found out it came from Twitter.

“I don’t think people really took it that seriously,” she said. “There are so many people that are doing that now.”

To keep passengers happy during the two-hour wait on the tarmac, Ellingen said their pilot gave updates every 10 minutes, sent the beverage cart through again and allowed bathroom breaks.

Kristine Schram of Bowler, Wisc., was on her way to San Diego for her grandson’s second birthday. The Twitter threat was “just crazy,” she said.

“I hope they find the guy,” she said. “It sounds like prison time to me.”

In recent days, unfounded bomb threats have also been made against Delta flights bound for Raleigh, N.C., and Tel Aviv.

A spokesman for Twitter told the AJC that the company may disclose a user’s account information to law enforcement in response to a valid emergency request. Twitter’s privacy policy says the company evaluates emergency disclosure requests on a case-by-case basis.

“If there is an exigent emergency involving the danger of death or serious physical injury to a person, we may provide information necessary to prevent that harm, if we have it.”

Twitter spokesman Nu Wexler told the AJC the company does not comment on individual accounts “for privacy and security reasons.”

“But we do work with law enforcement authorities on emergency requests for information in cases involving immediate danger,” Wexler said.

Staff writer Aaron Gould Sheinin contributed to this article.