A Libyan protester carries a gun as the American embassy burns

Libyan authorities have made four arrests in the investigation into the attack on the U.S. consulate in Benghazi in which the U.S. ambassador and three embassy staff were killed, the deputy interior minister said on Thursday.

"Four men are in custody and we are interrogating them because they are suspected of helping instigate the events at the U.S. consulate," Wanis Sharif told Reuters.

He gave no more details.

U.S. ambassador to Libya Christopher Stevens and three other Americans died after the gunmen attacked the U.S. consulate and a safe house refuge in the eastern city of Benghazi on Tuesday night. The attackers were part of a mob blaming America for a film they said insulted the Prophet Mohammad.

Demonstrators attacked the U.S. embassies in Yemen and Egypt on Thursday in protests against the film, and American warships were moved closer to Libya, reports Reuters.

President Barack Obama has vowed to bring to justice those responsible for the Benghazi attack, which U.S. officials said may have been planned in advance. Secretary of State Hillary Clinton said Washington had nothing to do with the video, which she called "disgusting and reprehensible".

"Any house that had any link to the Free Syrian Army has been destroyed," one resident said.

Residents returned to Tadamon to survey the damage, some of them hoping to retrieve family possessions. "I have come to take some of my goods," said a man on Daoul Street, looking at his partially destroyed house.

Distant explosions shook the district but there was no fighting in Tadamon itself on Thursday. Residents say they had been warned by the army that if they let rebels back in, soldiers would return to destroy the remaining houses.

"We haven't seen the Free Army since yesterday," said another resident.

In other parts of the capital, the violence is also taking a sectarian turn, reflecting the dangers of a conflict that is descending into outright civil war.