Tamil Tiger rebels launched suicide attacks against Sri Lankan troops fighting to deliver a death blow to the separatists after the president declared victory in Asia's longest modern war, the military said.

President Mahinda Rajapaksa returned to the country early on Sunday, the day after he said the Liberation Tigers of Tamil Eelam (LTTE) had been defeated militarily in the 25-year civil war, even as combat still raged in the island's northeast.

The military said it had rescued all the civilians being held by the LTTE as human shields, removing the last barrier to unleashing overwhelming firepower on the well-armed LTTE.

"All civilians from Vellimullivaikal have been rescued. The troops are still fighting the LTTE. Over 50,000 have been rescued since Thursday," military spokesman Brigadier Udaya Nanayakkara said.

The LTTE, founded on a culture of suicide before surrender, showed no sign of giving up in the face of an overwhelming military onslaught that has given no quarter in a relentless offensive nearing its third year.

Troops killed at least 70 Tiger fighters masquerading as civilians who tried to cross the Nanthikadal lagoon, on the western side of the battlezone, in six boats.

Blasts rocked the remaining rebel-held area, now measuring barely a square kilometre (0.5 sq mile), the military said.

"Suicide explosions are taking place. Suicide cadres are coming in front of troops in the frontline and exploding themselves," Nanayakkara said.

Government forces on Saturday took control of the entire island's coast for the first time since the war broke out in 1983, cutting off any chance of escape for a militant group whose conventional defeat has been a foregone conclusion for months.

Rumours swirled about the fate of Tiger founder-leader Vellupillai Prabhakaran and other senior leaders after a massive explosion was heard inside a bunker. Prabhakaran has in the past vowed not to be taken alive.

Nearly 37,000 people fled to army-held areas on Saturday, bringing the total since Thursday to more than 50,000. Before the exodus started, the United Nations had estimated there were 50,000-100,000 there.

Pro-rebel web site www.TamilNet.com reported that thousands of wounded people had been left to die after heavy weapons barrages, but it gave no sources.

"There has been no pause from continued cannon and heavy mortar fire," TamilNet said.

Getting an independent picture of events inside the war zone is normally a difficult task, given both sides have repeatedly distorted accounts to suit their side of the story and outside observers are generally barred from it.

The Tigers, whose fighters are said to wear cyanide capsules to be taken in case of capture, this week again refused to surrender or free civilians, while the government rejected calls to pause its assault to protect civilians.

Each side accuses the other of killing civilians, and diplomats say there is evidence both have done so. The UN rights chief on Friday said she backed an inquiry into potential war crimes and humanitarian violations by both sides.

A mounting wave of diplomatic pressure from the United States, Britain, France and the United Nations last week appeared to come too late to stop the final fight.

UN Secretary-General Ban Ki-moon's chief of staff, Vijay Nambiar, was due to meet government officials on Sunday to try to broker a negotiated end, a prospect seen as unlikely.

Rajapaksa, who was in Jordan on an official visit, landed in Sri Lanka early on Sunday and kissed the ground after he got out of the airplane, state TV showed.

Presidential officials speaking on condition of anonymity said he was due to make the formal declaration of victory in a nationally televised address either late on Sunday or Monday.

The date was then expected to be declared National Liber