Sri Lankans in Colombo on Monday buy newspapers to read about the army capturing the Tamil Tiger rebels' last major base on the northern war front. (Eranga Jayawardena/Associated Press)

Sri Lanka's army seized the Tamil Tiger rebels' last stronghold on Monday, but UN officials were worried about the dozens of civilian deaths that occurred during the fighting and the more than 150,000 civilians who remain trapped in the rebel-controlled territory.

Government forces captured Mullaitivu town, the rebels' last major base, on Sunday, leading some to believe the 26-year civil war in Sri Lanka may be coming to an end.

Since 1983, the Tamil Tigers have been fighting to create an independent state in the northeastern part of the Indian Ocean island. It's estimated that more than 70,000 people have been killed in the civil war.

The latest fighting has created a desperate situation for civilians, UN officials say.

"There have been many civilians killed over the last two days," said UN resident co-ordinator Neil Buhne. "It's really a crisis now."

It's estimated that between 150,000 and 400,000 civilians are trapped in the area where the rebels are still operating. At least 300 of those civilians have been wounded by artilley fire, a Sri Lankan health official said Tuesday.

The safety of the trapped civilians is of growing concern to human rights groups and diplomats, but the Sri Lankan government said the number of trapped is far lower than estimated.

Many have accused the rebels of preventing civilians from fleeing the area, while the government has accused the insurgents of using them as human shields.

Rebel officials could not be reached for comment because communications to the war zone, in the northern part of the country, have been cut.

The war zone is closed to most independent observers, including foreign journalists, and it is unclear how many civilians are trapped there.

But with the desperate rebels and civilians squeezed into a 299-square-kilometre area in the jungle, the situation has grown far more dangerous, officials said.

"It's a recipe for trouble … unless there's maximum restraint on both sides," Buhne said, adding civilians should be allowed to leave the war zone.

He said until recently both sides in the fighting worked hard to avoid civilian casualties.

Civilians are suffering from poor nutrition, no sanitation facilities and an inadequate water supply, he said. Some have been displaced as many as 15 times by the fighting, and many have dug trenches to take shelter during the shelling.

Last week, the government declared a "safe zone" in a small section of rebel-held territory and called on all civilians to move into that area, where they would be protected.

But there have been repeated reports of artillery fire in that region, and Buhne said there was regular fighting and shelling in the "safe zone" in recent days. The Sri Lankan military has repeatedly denied fighting in that area.

With files from the Associated Press