COLOMBO, Sri Lanka - The Sri Lankan military claimed Saturday it had destroyed a Tamil Tiger suicide boat, as the government ruled out a ceasefire in the northern war zone where hundreds of thousands of civilians are reportedly trapped.

The explosives-laden boat was intercepted by a naval ship and destroyed with heavy gunfire early Friday, according to the Defense Ministry Web site.

It said the boat was apparently launched from Mullaittivu and was headed for a naval blockade along the northeastern coast.

It gave no other details, and the Tamil Tiger rebels did not immediately respond to the claim.

The naval blockade is aimed at preventing the Tamil Tigers, cornered into a small 300-square-kilometre coastal territory north of Mullaittivu town, from escaping by the sea.

Their land escape routes are also sealed off by the Sri Lankan military, which has achieved a string of victories in recent months, ousting the Tigers from towns and villages.

The military believes it is now close to destroying the Tigers, who have been fighting since 1983 for a separate homeland for the minority Tamils in the north and the east.

But the fighting has also left many civilians trapped in the area controlled by the Tigers -- some 250,000 according to the Red Cross. But Human Rights and Disaster Management Minister Mahinda Samarasinghe disputed the figure, saying less than 120,000 civilians were in the war zone.

President Mahinda Rajapaksa had urged the rebels to let the civilians leave the conflict zone by Saturday and guaranteed safe passage to all noncombatants. But the government insisted there would be no let up in its war.

"We are determined not to have a ceasefire, and we are determined to eradicate terrorism in Sri Lanka," Samarasinghe told reporters Friday.

He denied reports that more than 300 civilians were killed in recent fighting and accused the rebels of forcibly recruiting civilians, giving them two or three days of training and putting them on the front line as cannon fodder.

"We have not targeted civilians and we will not target civilians," he said.

Tamil Tiger spokesman Balasingham Nadesan said the government has stepped up artillery attacks on civilian areas, leaving at least 28 people dead Friday.

"Only a permanent ceasefire mooted by the international community and (ensuing) negotiations would resolve the conflict," he said on a pro-rebel Web site, TamilNet.

Human rights groups accuse the rebels of holding the civilians hostage and the military of launching heavy attacks in civilian-filled areas, including a government-declared "safe zone."

UNICEF said many children -- some just months old -- have been injured, killed or are living in poor conditions.

More than 70,000 people have been killed in the civil war, which grew out of complaints by Tamils, who have suffered decades of marginalization at the heads of successive governments controlled by the Sinhalese majority.

Observers say even if the Tigers are vanquished on the ground the insurgency will not end.

"It is time for Sri Lanka to pick up the pieces of peace negotiations with Tamils ... and work for a political settlement," wrote Haridas Ramakrishnan in a column in the state-owned Daily News newspaper.