TRIPOLI (AFP) - At least two people were killed and 25 wounded as militiamen opened fire Friday on residents holding a peaceful protest to demand they vacate their Tripoli headquarters, a Libyan official said.

The militias are holdovers from the 2011 uprising that ousted dictator Muammar Gaddafi and now a powerful force in the increasingly lawless North African country.

"Two dead and 25 wounded have so far been admitted to Tripoli hospitals," a Health Ministry official told AFP, asking not to be named, in what he termed a provisional toll.

Mr Sadat al-Badri, president of the Tripoli local council, or town hall, who had called for the protest, told AFP the shots fired at the hundreds of demonstrators came from inside the headquarters.

"Tensions are on the rise in Tripoli. We're going to announce a general strike and launch a civil disobedience campaign until these militias leave," he said.

At the weekly Muslim prayers held hours earlier, imams in their sermons backed the call to protest against militias issued by the town hall as well as Libya's mufti, the highest religious authority.

Hundreds of people carrying white flags in a sign of peace, as well as the national flag, and singing the national anthem had assembled in the capital's Meliana Square.

They then marched to the Misrata militia headquarters in the Gharghour district to press their demands when gunmen inside fired into the air to scare them off.

When the crowd continued to approach the building, the gunmen started firing at them, said an AFP correspondent who saw two wounded, including one hit in the stomach.

A leader of the militia from Misrata, east of the capital, told private television channel Al-Naba that the demonstrators had opened fire first.

The march was sparked by violence on Nov 7 in which the Misrata militia also played a central role, illustrating again the instability of Libya.

One of the group's leaders Nuri Friwan had been fatally wounded in fighting at a checkpoint manned by other former rebels, and two people were killed in subsequent fighting.

One Western diplomat said the situation was becoming "increasingly critical", and the British, French, Italian and United States embassies issued a joint statement calling for Libyans to "put aside their differences".

Residents of Tripoli frequently demonstrate against the militias, who have rejected calls from a weak central government to leave the capital.

Just weeks ago, armed men seized Prime Minister Ali Zeidan and held him for several hours before releasing him.

The head of an Interior Ministry anti-crime unit later boasted that he was behind the "arrest" and that he was "proud" of it.