A barrage of bullets and two car bomb blasts rattled Mogadishu on Sunday when nine al-Shabab Islamic extremists stormed Somalia’s main court complex, officials said, in a two-hour attack that shows the country’s most dangerous militant group may be down but not defeated.

A preliminary death toll stood at 16, including all nine attackers. The government didn’t immediately publicize the number of security forces, government employees and civilians who died during the attack.

The assault was the most serious in Mogadishu since al-Shabab was forced out of the capital in August 2011. Al-Shabab controls far less territory today than in recent years, and its influence appears to be on the decline, but Sunday’s attack proved the extremists are still capable of pulling off well-planned, audacious assaults.

The top U.N. official for Somalia, Augustine P. Mahiga, said he was shocked and outraged by the attack. Mahiga said the total number of dead wasn’t clear, but that reports indicated that “many innocent civilians were killed including women and at least one child.”

The attack on the Supreme Court complex began at around 12:30 p.m., sparking running battles with police and army forces. One car bomb detonated outside the court, and gunmen were seen on the roof of a court building firing shots. Police officer Hassan Abdulahi said he saw five dead bodies lying at the entrance to the court.

The militants took an unknown number of hostages during the siege. Many other government workers and civilians in the court complex — a confusing labyrinth of buildings and rooms — hid while fearing for their lives.

Western officials knew militants had been planning a major violent incident. The British Foreign Office on Friday released a travel warning for Somalia that warned of a high threat of terrorism. “We continue to believe that terrorists are in the final stages of planning attacks in Mogadishu,” it said.

The complex and sustained nature of the assault on the court system suggested the extremists hoped to inflict severe casualties. Later, a suicide car bomber rammed a vehicle carrying Turkish citizens, killing two.

On a Twitter feed believed to belong to the militants, al-Shabab appeared to take credit for the attack. A posting said five militants from the “Martyrdom Brigade” took part in the “daring” attack.

“Such brazen attacks, on a broad daylight and in the heart of Mogadishu, are a clear testament to the influence of HSM forces in the capital,” one posting said. HSM is an abbreviation for al-Shabab.

Nine militants attacked the court complex, and that six of them detonated suicide vests, said Interior Minister Abdikarim Hussein Guled. The three others were shot and killed during the assault, he said. Guled said he couldn’t immediately provide an overall death toll.