Washington confirmed it was rushing military supplies to the Lebanese army but the Lebanese opposition warned the government against getting involved in a US-backed war against the al-Qaeda-inspired fighters of fringe Palestinian militant group Fatah al-Islam.

Relief agencies expressed growing concern for the 10,000 or so civilians still inside the Nahr al-Bared camp outside Lebanon's second city of Tripoli whom the army has said are being used as "human shields" by the militants.

As a fragile truce unilaterally declared by the militants on Tuesday largely held, Defence Minister Elias Murr said talks were under way to try to reach a negotiated end to the siege.

"We are now giving a chance for political negotiations," he told reporters late on Friday.

But he added: "If the political negotiations fail, I will leave it up to the army command to carry out the required actions."

Murr did not specify who was brokering the talks but reports said mainstream Palestinian factions were trying to break the deadlock for fear of the impact that an all-out offensive against the camp would have on Palestinian civilians.

By longstanding convention, the army does not enter Lebanon's 12 refugee camps, leaving security inside to the Palestinian factions.

Previously, Murr had ruled out any negotiations to end the clashes, which have killed 78 people, 33 of them Lebanese soldiers, in the worst internal strife since the 1975-90 civil war.