Sri Lanka's government said Monday that Tamil separatists must lay down their arms before ceasefire negotiations can begin, as the military continued heavy ground and air attacks on the guerrilla de facto state in the north.

"We can't trust them with arms in their hands," government spokesman Keheliya Rambukwella said, accusing the Tamil Tiger rebels of using a previous truce to rebuild their strength.

On Sunday, a rebel-affiliated Website reported that the Tigers were willing to consider a ceasefire. The government has recently stepped up an offensive aimed at ending the group's 25-year-old civil war, which has killed more than 70,000 people.

"There is no hesitation on our side to reiterate our position that we have always wanted a ceasefire," the TamilNet site quoted rebel political wing head Balasingham Nadesan as saying.

Nadesan said the rebels were only fighting a defensive war that the government has forced them into, TamilNet reported.

The government officially withdrew earlier this year from a nearly 6-year-old Norwegian-brokered cease-fire that had been openly violated by both sides.

Rambukwella said the government had "enough experience"

with Tamil Tiger truces, and that every time the rebels "get weakened militarily, they call for a cease-fire and within the process, they get strengthened. "

The rebels "should lay down arms before any negotiations," he said.

In recent months, government troops have made dramatic progress in fighting against the rebels in the north, seizing a series of guerrilla bases and chunks of land, but the rebels have offered stiff resistance.

The military says army troops are closing in on • the rebels' administrative capital, Kilinochchl.

On Sunday, air force fighter jets hit a rebel artillery gun posi-

tion and a command centre near Kilinochchl, air force spokesman Janaka Nanayakkara said. Army troops also pushed into the rebel stronghold of Ponneryn in the north, causing heavy damage to the guerrillas, the military said. It did not provide details of casualties.

Rebel officials were not available for comment because most communication lines to guerrilla-held areas have been severed.

The Tamil Tigers have been fighting since 1983 to create an independent homeland for ethnic minority Tamils, who have suffered marginalisation at the hands of successive governments controlled by ethnic Sinhalese.