The U.S. Justice Department has filed the first criminal charges in the deadly attack on the U.S. diplomatic mission in Benghazi, Libya, two U.S. officials said Tuesday.

The officials confirmed that a sealed complaint was filed in U.S. District Court in Washington against an unspecified number of individuals in the September 2012 attack that killed Ambassador Chris Stevens and three other Americans. One official said those charged included Ahmed Abu Khattala, the head of a Libyan militia. The officials spoke on condition of anonymity because they were not authorized to discuss a sealed indictment.

Libyan security forces on Saturday arrested two men for firing at a military patrol in Benghazi, a commander in Libya's special forces told Agence France Presse.

"Two individuals on board a vehicle opened fire on Saturday on a special forces unit stationed in Benghazi city center," Colonel Wanis Boukhamada said.

Clashes between Libyan elite forces and gunmen killed six soldiers in Benghazi on Saturday, the army said, in the latest bout of unrest as the government struggles to control rebels from the 2011 uprising.

The interim leader of Libya's army warned of the danger of a "bloodbath" as the unrest in Benghazi flared again a week after violence killed more than 30 people in the eastern city.