COLOMBO, Sri Lanka - Sri Lanka's prime minister said the reclusive leader of the separatist Tamil Tigers was trapped in a tiny stretch of coastline surrounded by government troops and vowed Tuesday not to let him slip away.

In recent months government forces ousted the rebels from their strongholds across the north. The army say the Tigers are cornered in a sliver of land just 4 kilometres long on the northeast coast along with tens of thousands of civilians.

Citing intelligence reports, Prime Minister Rathnasiri Wickremanayake told Parliament that rebel chief Velupillai Prabhakaran "remains trapped" in the rebel-held territory, confirming the assertion a rebel official made last week in an interview with The Associated Press.

"Security forces have taken all possible steps to ensure that he won't get away," Wickremanayake said, in response to a question from the opposition.

International pressure has grown for a humanitarian truce to protect an estimated 50,000 civilians still trapped in the war zone. Aid and rights groups accuse the rebels of holding the civilians as human shields, a charge the rebels deny.

Wickremanayake reiterated the government would not accept a truce, because it would allow the rebels to regroup, and lashed out at foreign diplomats calling for a halt in the fighting.

"Various puppets who claim to be experts are trying to prevent this terrorist from being captured alive. Some are calling for a cease-fire. But we as a government are not prepared to bow down to these forces," Wickremanayake said.

Last week, the foreign ministers of Britain and France made a rare visit here to call for a truce. On Tuesday, a delegation of five British lawmakers was in Sri Lanka to meet with officials, the opposition, aid groups and travel to displacement camps in the north.

The UN said Tuesday it remained concerned about the fighting in the war zone, adding that "fighting has intensified with both light and heavy weapons being used," Elisabeth Byrs, spokeswoman for the UN humanitarian office, said in Geneva.

The government promised last week to stop using heavy weapons out of deference to the civilians in the region. However, there have been persistent reports of continued shelling.

More than 188,000 ethnic Tamil civilians have crossed over the front lines in recent months, overwhelming displacement camps in the north, Byrs said. The UN has received about one-third of the US$155 million it estimates it needs to deal with the emergency, she said.

The rebels said in a statement Tuesday that civilians trapped in the war zone were facing starvation and accused the government of blocking food deliveries.

It said ethnic Tamil expatriates were planning a humanitarian aid delivery to the war zone and called on the UN and other governments to give "moral, political and logistical support."

Human Rights Minister Mahinda Samarasinghe dismissed the rebel allegation as an "absolute propaganda ploy." He said the government had delivered enough food and accused the rebels of grabbing the supplies for themselves.

Government forces pushed 250 metres further into the rebels' remaining territory Tuesday, inflicting heavy damage on the insurgents, the military said. It made no mention of civilian casualties.

Reporters and independent observers are barred from the war zone making the government's claims difficult to verify.

The rebels have been fighting since 1983 for a separate state for minority Tamils, which have suffered decades of marginalization at the hands of governments controlled by the Sinhalese majority.