Ahmed Abu Khattala, one of the suspected Libyan ringleaders of the 2012 terrorist attacks in Benghazi that killed four Americans, is in federal law enforcement custody at E. Barrett Prettyman U.S. Courthouse in Washington. A U.S. marshal patrols outside the courthouse.

June 28, 2014 Ahmed Abu Khattala, one of the suspected Libyan ringleaders of the 2012 terrorist attacks in Benghazi that killed four Americans, is in federal law enforcement custody at E. Barrett Prettyman U.S. Courthouse in Washington. A U.S. marshal patrols outside the courthouse. Sarah L. Voisin/The Washington Post

In September 2012, a U.S. diplomatic compound and CIA annex in Benghazi, Libya, were attacked, killing four Americans.

A year after the fall of longtime dictator Moammar Gaddafi, on Sept. 11, and 12, 2012, a U.S. diplomatic compound and CIA annex in the Libyan city of Benghazi were attacked, killing four Americans, including U.S. Ambassador J. Christopher Stevens.

A year after the fall of longtime dictator Moammar Gaddafi, on Sept. 11, and 12, 2012, a U.S. diplomatic compound and CIA annex in the Libyan city of Benghazi were attacked, killing four Americans, including U.S. Ambassador J. Christopher Stevens.

A clandestine raid by U.S. Special Forces to capture the chief suspect in attacks on an American diplomatic outpost and CIA compound in Benghazi in 2012 has underscored the fragility of the central Libyan government’s authority, intensifying concerns here about growing instability in the country as Islamists and rebel army forces clash in the east.

The operation Sunday to apprehend Ahmed Abu Khattala, 43, was “unilateral,” U.S. officials said. The move appeared to slight Libya’s fledgling security institutions, which have been unable to rein in the powerful militias and Islamist extremists that have plagued Benghazi since the 2011 uprising, although Libyan officials acknowledged Tuesday that their forces were not up to the task.

“The government’s inability to go after people like this has put us in a situation where we have to accept such raids,” said Mohamed Abdullah, a member of Libya’s General National Congress.

Abu Khattala is accused by a U.S federal court of being involved in the killing of four Americans, including Ambassador J. Christopher Stevens, in the attacks on Sept. 11, 2012. “We have failed to build a proper institution that can be trained and equipped and prepared for such an operation,” Abdullah said.

Libya’s national army and police are more a patchwork of militias than a unified force with a central command.

U.S. Special Operations forces have captured Ahmed Abu Khattala, an alleged ringleader of the 2012 attacks on the U.S. diplomatic compound in Benghazi, Libya. Here is what is known about Abu Khattala. (The Washington Post)

The Special Forces raid comes amid renewed fighting in Benghazi between the militant Ansar al-Sharia group, to which the United States says Abu Khattala is linked, and armed forces loyal to renegade Libyan general Khalifa Hifter. After fighting in the rebellion against authoritarian leader Moammar Gaddafi in 2011, Hifter launched a rebel campaign in May to eradicate the Islamists whom many in Benghazi blame for a string of assassinations in recent years.

On Sunday, airstrikes carried out by pilots loyal to Hifter sparked clashes with armed militias, including Ansar al-Sharia.

According to residents in Benghazi, including some of Abu Khattala’s close neighbors, Abu Khattala had joined the battle against Hifter and had been out fighting Sunday before U.S. forces captured him.

“He came back home around sunset, and he looked tired and dirty,” said a man who lives across the street from Abu Khattala’s family home in the al-Lathi district and spoke on the condition of anonymity for fear of reprisal from militant groups in the city. “That was the last time any of us [in the neighborhood] saw him.”

Benghazi residents said the city was tense following the news of Abu Khattala’s capture, despite widespread support for Hifter’s military actions against Ansar al-Sharia.

Hifter was not involved in the capture, the State Department said Tuesday, and the former general and his deputy commander were unavailable to comment Tuesday night. A Libyan government spokesman also declined to comment on the operation and whether authorities had been informed.

“I wish that Americans and others would respect Libyan sovereignty,” said Mohamed Abu Sidra, a Salafist Islamist member of the national congress. “This isn’t the first time” U.S. forces have carried out a raid, a reference to the abduction in the capital, Tripoli, in October of Nazih Abdul-Hamed al-Ruqai, who is accused of taking part in the 1998 bombings of U.S. embassies in East Africa.

Concern was voiced in Tripoli on Tuesday that Ansar al-Sharia or others supportive of Abu Khattala would take aim at the U.S. government or Libyan authorities because of the capture.

“There could be a backlash,” said Abdullah, the congress member. “They could go after the U.S. or U.S. interests, possibly. Or even attempt to go after the Libyan government.”

But as news of the arrest spread, many Tripoli residents said they approved of the U.S. operation.

“The Americans did a favor for us with this raid. I wish they had taken them all,” Mohammed, a patron at a cafe in central Tripoli, said of the extremists. Mohammed declined to give his full name, saying he fears retaliation from pro-Islamist militias. “There is no government here. If the Americans come back to arrest more, I will go with them,” he said.

Mohammed’s friend Khaled, also a Tripoli resident, wasn’t as enthusiastic.

“America is responsible for bringing the extremists here,” he said, accusing the United States of enabling the Islamists’ rise to power following the Arab Spring. “So they are responsible now for taking them out.”

Nizar Sarieldin contributed to this report.