In this photo released by the Sri Lankan army on Tuesday, ethnic Tamil civilians who left Tamil Tiger-controlled areas are seen arriving on Monday at the government-controlled areas in Putumattalan, northeast of the Sri Lankan capital, Colombo. (Sri Lankan army/Associated Press)Sri Lanka's Tamil rebels say some 1,000 civilians were killed and more than 2,000 were injured when government troops raided their last sliver of territory on Monday to allow tens of thousands of civilians to flee the coastal strip.

The Tamil Tigers said in an emailed statement on Tuesday that a "bloodbath" prevails in the war zone, calling on the United Nations and the world community to act to rescue the trapped civilians.

The military denies the allegation, and has accused the rebel group of targeting civilians leaving the conflict zone in a desperate attempt to use them as human shields against advancing government troops.

Government forces said they rescued thousands of civilians on Monday after they broke through a barrier built by the rebels to protect their territory. By Tuesday evening, the military said 52,000 civilians had escaped.

It's not possible to obtain independent accounts of the situation because the war zone is off-limits to journalists.

A government deadline of noon local time Tuesday for the Tamil Tigers to surrender passed without word from the rebel group. Hours later, a spokesman for the rebels vowed in an interview with Reuters that the Tigers would "never surrender."

Tens of thousands of civilians were still confined to a rapidly shrinking territory declared a "no-fire zone" by government forces, the International Committee of the Red Cross said in a statement.

The Red Cross called for "exceptional precautionary measures" from both sides to minimize further mass civilian casualties.

Group concerned about artillery

Pierre Krahenbuhl, director of operations for the Red Cross in Sri Lanka, described the situation in the area as "nothing short of catastrophic."

"What we are seeing is intense fighting in a very small area overcrowded with civilians who have fled there," Krahenbuhl said.

He said the group is "particularly concerned" about the use of artillery and its impact on civilians.

The Tigers have been fighting since 1983 for an independent state for the Tamil minority, which they say suffered decades of marginalization at the hands of governments dominated by the Sinhalese majority. An estimated 70,000 people have been killed in the fighting.

Government forces say they are close to crushing the separatists after a blistering offensive in recent months in the country's war-ravaged north.

The rebel group is officially banned in Canada since the Conservative government listed the Tigers — known formally as the Liberation Tigers of Tamil Eelam (LTTE) — as a terrorist organization in 2006 for its reported use of suicide bombers and child soldiers during the civil war.

With files from The Associated Press