Two of Europe's top diplomats visiting Sri Lanka on Wednesday called for an immediate ceasefire in the South Asian nation's northern region to allow tens of thousands of trapped civilians to escape the conflict zone.

British Foreign Secretary David Miliband and French Foreign Minister Bernard Kouchner also called on the Sri Lankan government to allow aid workers to enter the tiny coastal strip of land where an estimated 60,000 civilians remain trapped.

"Now is the time for the fighting to stop," Miliband told reporters in the capital, Colombo.

However, Kouchner said Sri Lanka's government denied their request.

The two men were on a one-day visit to Sri Lanka representing the European Union and were later heading to visit a camp for war refugees.

Sri Lanka earlier denied entry to Swedish Foreign Minister Carl Bildt, who was due to join the diplomatic mission.

A UN report released last week put the number of noncombatants killed in the government's recent offensive against Tamil Tiger rebels, known formally as the Liberation Tigers of Tamil Eelam, at almost 6,500.

The military has the LTTE guerrillas surrounded in the 12-kilometre-long strip, and has accused the rebels of using civilians as human shields.

The Tigers say they're calling for a ceasefire because an unprecedented humanitarian crisis is unfolding. The rebels also accused government forces on Tuesday of breaking a pledge to refrain from using heavy weaponry by firing artillery shells into their territory.

Aid groups say some of the trapped civilians are dying of starvation.

The rebels have been fighting to create an independent homeland for ethnic minority Tamils, who they say have faced decades of marginalization by governments controlled by the ethnic Sinhalese majority.

Some 70,000 people have been killed in the country's 25-year civil war, although observers and aid groups fear the toll could be much higher.

With files from The Associated Press