Tripoli, Libya (CNN) -- In a move disavowed by the Libyan government, a retired military general led Libyan troops and other forces loyal to him in a deadly attack Friday against Islamist militants in and around the eastern city of Benghazi, Libyan media reported.
At least 12 people were killed and 91 others were injured in clashes around the country's second-largest city, Libyan state news agency LANA said Friday, citing local hospitals.
Retired Libyan Gen. Khalifa Haftar, who participated in the 2011 rebellion that ousted dictator Moammar Gadhafi, launched the attack that supporters said was an attempt to clear the city of extremist groups, CNN affiliate Libya Awalan TV reported.
The Libyan government and the military command in Tripoli reacted with alarm, saying that they didn't order the attack, and that the operation -- which they conceded included some Libyan soldiers -- amounted to a "coup."
That such a force could mount an attack without the government's blessing underscores the difficulty that Tripoli -- more than 400 miles to the west -- has had in trying to influence a dire situation in Benghazi, where Islamist groups have been blamed for near daily assassinations, bombings and kidnappings against security forces.
A Libyan air force plane and 120 military vehicles took part in the unauthorized operation against the militants, acting Prime Minister Abduallah al-Thinni said on Libyan state-run TV.
Residents of Benghazi, meanwhile, told CNN that they saw more than one military plane overhead Friday. It wasn't clear how many of the operation's fighters were members of the North African country's military.
"Their movements are against military orders issued by the legitimate authorities," al-Thinni said, adding that he felt the move undermined government-sanctioned efforts to fight militants in Benghazi.
Haftar led the operation, Libyan army Chief of Staff Abdul Salam Jad said, describing the attack as an "attempted coup on legitimacy," according to Libya's official LANA news agency.
Retired general had promised action
Haftar was a commander under Gadhafi before the general defected in the 1980s. Haftar was in exile in the United States until he returned for the 2011 rebellion.
In recent months, Haftar toured cities in eastern Libya, promising some kind of military offensive to purge Benghazi -- the cradle of the 2011 revolution against Gadhafi -- of Islamist extremist groups.
Haftar's overtures came amid rising frustration in Benghazi that Tripoli hasn't been able to staunch radical Islamist militant groups' presence and influence, which has been rising since the revolution.
Residents and officials have blamed the violence that has gripped Benghazi on groups including Ansar al Sharia.
The United States designated that group a terrorist organization this year, and has accused it of being involved in the 2012 attack that killed four Americans -- including Ambassador Christopher Stevens -- at a U.S. diplomatic compound in Benghazi.
Official Libyan security forces have struggled to deal with hostile militias, so the government has relied on other militias, many on the state's payroll, in an attempt to enhance security. But various other political forces also have relied on militias, leaving the country awash in armed groups -- many who refused to disband after the revolution -- with competing agendas and loyalties.
Al-Thinni called on government-sanctioned militias Friday to "practice self-restraint" and keep abiding by the Army's orders,
"The government calls on the people in the capital of the revolution, Benghazi, to be calm and (to) support the legitimacy of the ... revolution and its police and army," al-Thinni said on state TV.
Algeria temporarily closes embassy in Tripoli, citing unspecified threats
Meanwhile, Algeria temporarily closed its embassy and consulate in Libya's capital due to a "real and imminent threat" against its diplomats and consular staff in Libya, the Algerian Foreign Ministry said Friday, according to Algerian state-run news agency Algerie Presse Service.
The ministry described the move in Tripoli as an "urgent and protective measure in coordination with Libyan authorities after receiving confirmed information about a real threat against our diplomats and consular staff," according to APS.
Libyan government officials were not immediately available for comment.