Sri Lankan President Mahinda Rajapaksa has promised the United Nations that his forces would protect Tamil civilians as it pushes ahead with its offensive to defeat the Liberation Tigers of Tamil Eelam.

Rajapaksa gave this assurance over telephone to UN Secretary General Ban ki Moon [Images], as his forces overran the last base of the sea Tigers near Mulaittivu, cutting off all their escape routes.

The President's words that his military will protect the non-combatants also come at a time when there have been reports of mounting civilian casualties in the war zone, where an estimated 250,000 civilians are trapped.

"Rajapaksa told the UN Secretary General that the current military operations to defeat terrorism in Sri Lanka [Images] would be carried out without harassment to the civilian population in the north," an official release said.

President Rajapaksa gave the Secretary General an update on the progress of operations against the LTTE [Images] and the situation regarding the civilians in the affected areas in the north of Sri Lanka, it said.

International pressure has been building up recently, asking Colombo to enforce a 'no-fire' period to allow trapped civilians to move to safer areas. But Lankan authorities have rejected the proposals, saying the military operations would be carried on.

Meanwhile, a military spokesman said at least 300 civilians had crossed the frontline into the government-designated 'safe-zones' during the past 24 hours and another 300 were waiting to come over. Military spokesman Udaya Nanayakkara said that this cross-over could become bigger.

The Lankan leader told the Secretary General that his forces were carrying out operations against a 'brutal terrorist outfit, which was holding the civilians as human shields'.

The government considered freeing of Tamil people from the clutches of terror as its responsibility, Rajapaksa said. In the 15-minute telephonic talk, Rajapaksa also brought to the attention of Ban his government's offer to the Tigers to lay down arms and surrender.

He said that the LTTE had not responded to these offers as well as suggestions made by the Tokyo 'co-chairs' to seek modalities for ending hostilities. Earlier in a statement, Ban had called on the LTTE and the government to accord 'immediate and absolute priority' to ensuring the protection and well-being of civilians, including humanitarian aid workers.

The Secretary General also called on both parties to respect 'no fire zones' and civilian infrastructure including schools, medical facilities and humanitarian facilities and assets.