BEIRUT (AFP) -- Lebanese Prime Minister Fuad Siniora repeated a warning on Saturday to Islamist militants holed up in a northern refugee camp that they must surrender or be crushed, as intense fighting continued to rage. "This is a terrorist gang," Siniora said of Fatah al-Islam in an interview with Al-Arabiya television. "They have to surrender themselves and their arms." He said that if the Islamists give up "they will face a fair trial," but added that the army was carrying out missions against the Nahr al-Bared camp "like surgical operations in order to eradicate this phenomenon."

Earlier a spokesman for the militants had vowed that they would fight to the last man.

Siniora said the camp's population had fallen from more than 31,000 to fewer than 3,000, including the gunmen, after civilians fled following the outbreak of fighting on May 20.

He accused Fatah al-Islam, which he said had about 250 men, of preventing remaining civilians from leaving the camp in an apparent bid to use them as human shields. Earlier, an army spokesman said "the battles will continue until we put an end to the phenomenon" of Fatah al-Islam. "The only choice for the gunmen is to give themselves up." The army said it wanted a "quick end" to the crisis and called on the militants to "return to reason."

But Fatah al-Islam spokesman Abu Salim Taha vowed: "We will not surrender and we will fight until the last drop of blood.

"The Nahr al-Bared camp will not fall despite the destructive shelling, and the army will not be able to enter," Taha told AFP.

Troops on Saturday, the 14th day of the battle, were pounding Nahr al-Bared with 155mm artillery fire, an AFP correspondent said.

Batteries of big guns on high ground targeted the northwest of Nahr al-Bared, where most of the militants were believed to be entrenched.

Two helicopters also used heavy machineguns to attack militants, the first time choppers have been used in the battle.

An AFP photographer said the helicopters made about a dozen passes above positions manned by Fatah al-Islam, who replied with anti-tank rockets without hitting either aircraft.

Sheikh Mohammed al-Hajj, a member of a delegation of Palestinian clerics attempting to broker a negotiated solution, called for a halt to the shelling.

But the Islamist Hamas movement of Palestinian prime minister Ismail Haniya said the "tangible progress" made by the army in clearing the camp's northern and eastern edges of militants might help mediation efforts.

"This is a victory that could open the way for a political settlement," spokesman Ali Baraka said. An army spokesman said "our soldiers have cleaned up pockets of resistance around the north and east sides of the camp, and sappers have made safe buildings booby-trapped by Fatah al-Islam on the edges of the camp before they can be dislodged."

The military earlier confirmed losing six soldiers in 36 hours, taking to 94 the death toll since the fighting erupted on May 20 -- 41 of them soldiers -- in Lebanon's deadliest internal conflict since the 1975-1990 civil war.

A mainstream Palestinian commander inside the camp said at least eight militants had been killed on Friday, but that there were no casualties among civilians, as they were sheltering in areas under his control.

"Southern districts have been completely spared bombardment by the Lebanese army -- that's why there have been no victims among civilians," said Abu Imad Halwani, regional commander of the Fatah movement of Palestinian President Mahmud Abbas.