COLOMBO, Sri Lanka - Sri Lanka's separatist rebels asked Britain and France to keep pushing for a ceasefire in the island's civil war after the European nations' recent failure to secure a halt in the fighting to allow civilians to evacuate.

The Tamil Tiger rebels' political head, Balasingham Nadesan, wrote Saturday to British Foreign Secretary David Miliband and his French counterpart, Bernard Kouchner, saying the insurgents are ready to "engage in the process to bring about a ceasefire and enter into negotiations for an enduring resolution to the conflict."

Excerpts of Nadesan's letter were e-mailed to news organizations.

International concern has grown in recent weeks about the fate of an estimated 50,000 noncombatants trapped in a tiny coastal strip along with the cornered rebels. A recent United Nations report said about 6,500 civilians were killed in the area during the past three months.

Miliband and Kouchner visited Sri Lanka last week to press for a truce, but the government refused to let up its offensive, saying it is on the verge of crushing the rebels' decades-old separatist war.

Fighting continued Sunday. The military said it captured a 500-metre-long earth fortification erected by the rebels to slow the army's advance.

Military spokesman Brig. Udaya Nanayakkara said the rebels were now confined to just a 4.5-kilometre coastal stretch. He did not give casualty details from the battle.

Pressure for a cease-fire is likely to increase after a pro-rebel website reported Saturday that government forces shelled a makeshift hospital in the war zone, killing 64 patients and bystanders.

A government doctor working there confirmed the death toll but declined to say who was responsible for the attack.

The government denied the report. Though it has refused to call off its troops' advance, it did promise not to use heavy weapons in the densely packed conflict zone, where it says the rebels are holding civilians to use as human shields in their final stand.

The rebels have fought since 1983 to create an independent homeland for ethnic minority Tamils, who have suffered decades of marginalization by successive governments controlled by majority ethnic Sinhalese. More than 70,000 people have been killed in the violence.

In his letter, Nadesan sought "recognition and the support" from the world community for their fight.

The rebels are banned by the United States and the European Union as a terrorist organization.