A gun fight erupted in central Tripoli on Tuesday, killing two, as a group of former rebels from the western city of Misrata clashed with a unit of ex-fighters from the Libyan capital, witnesses said.

The two groups of former rebels who helped topple the regime of slain leader Moamer Gathafi traded anti-aircraft and heavy machinegun fire as they fought in broad daylight in a Tripoli neighbourhood.

The fighting broke out between Al-Zawiyah and Al-Saidi streets near a building used as intelligence headquarters by the former regime.

Reporters saw the building and the entire neighbourhood surrounded by hundreds of rebels who ousted Gathafi, several of them armed with Kalashnikovs, amid steady gunfire.

Massud al-Khadar, a member of a militia from the neighbourhood, said: "Two of our (fighters) were killed in the clashes which began this morning."

He said the violence started when a rival militia from Misrata attacked his group based near the former intelligence building.

Ex-rebels, who remain organised in militia brigades, are visible in many parts of the capital, and some have taken control of former government buildings to use as headquarters.

But witnesses said earlier that forces linked to the new government's interior ministry may have tried to retake the intelligence building on Tuesday, provoking a clash with the militia group occupying it.

Those reports could not be independently verified, and the interior ministry declined to comment, saying it would comment on the clashes later Tuesday.

Sources saw militiamen had blocked traffic from reaching the building, even as ambulances tried to access the area, with witnesses reporting a number of injuries.

Many gunmen could also be seen circulating in the area and the situation remained chaotic.

A vehicle belonging to a former rebel group based in the area and equipped with a microphone and loudspeakers was touring the neighbourhood's streets, urging residents who are not armed to leave.

The presence of armed militia groups in Tripoli is one of the biggest challenges facing the new Libyan rulers.

These groups, several of them from outside Tripoli, fought Gathafi's forces while liberating the capital in August. Since then, they have stayed put in the city and refused to return to their home towns.

In the absence of proper security forces, these militias are offering security on the streets of Tripoli. Powerful militias from Misrata and towns such as Zintan, southwest of Tripoli, are even guarding key installations in the capital.

Tripoli residents, however, have been protesting against their presence, saying it has actually raised security concerns in the capital.

Several militia commanders have said their fighters would leave Tripoli only when a new national army is formed.

Prime Minister Abel Rahim al-Kib has acknowledged the issue as a "complex" one, saying tens of thousands of the former rebels would be integrated into the security forces.