A gunbattle has erupted between hundreds of revolutionary forces and Muammar Gaddafi supporters in the Libyan capital for the first time in more than two months.
The fighting began when a group of loyalists carrying the green flag symbolising the ousted leader's regime appeared on the streets of Tripoli's Abu Salim neighbourhood, which houses the notorious prison of the same name.
Shouting "God is great", anti-Gaddafi fighters converged on the area, which has long been a loyalist stronghold, in pick-up trucks mounted with weapons, setting up checkpoints as heavy gunfire echoed through the streets.
The violence in the capital, which has been relatively calm since then-rebels seized control in late August, underscored the difficulty Libya's new rulers face in restoring order as Gaddafi remains on the run. He has issued several audio recordings from hiding trying to rally supporters against the North African nation's transitional leadership.
Witnesses said the shooting began after a group of dozens of men and women tried to raise the green flag at the end of a street in the Hay Nasr district.
"I looked out of my window and I saw men and women in a group of 50 to 80 people carrying the green flag," said Abadi Omar, a resident in one of the buildings in the area. "They put one of these flags at the end of our street. This is when the rebels came out and these people disappeared."
Revolutionary forces started searching every building in the area and found weapons on some of the rooftops, many hidden under water tanks, Mr Omar said. Then snipers opened fire and the gunbattle began as anti-Gaddafi fighters gave chase around the closely packed buildings.
In Geneva, a senior UN human rights official expressed concern about a risk of serious abuses against suspected loyalists occurring when Gaddafi's last strongholds fall to revolutionary forces. The head of the UN human right's office's rule of law section, Mona Rishmawi, said Libya's transitional government is trying to ensure the rights of captured Gaddafi fighters are protected but "the system that is currently in place is not adequate".
Fighters in Sirte pounded loyalists holed up in two neighbourhoods with rocket and machine-gun fire, but also suffered heavy casualties themselves, with wounded men streaming into frontline medical units, then being evacuated to field hospitals on the city's outskirts.
Libya's new rulers have insisted Sirte's fall is imminent and they expect to declare liberation this week. That could allow them to name a new interim government and set a timeline for holding elections within eight months.