How effective is UN? | Life inside no-fire zone | Sowing seeds of new conflict | Plenty of firepower | Government's lies | Bunkers and carnage | Leading article | Graphic: Map of no-fire zones

More than 20,000 Tamil civilians were killed in the final throes of the Sri Lankan civil war, most as a result of government shelling, an investigation by The Times has revealed.

The number of casualties is three times the official figure.

The Sri Lankan authorities have insisted that their forces stopped using heavy weapons on April 27 and observed the no-fire zone where 100,000 Tamil men, women and children were sheltering. They have blamed all civilian casualties on Tamil Tiger rebels concealed among the civilians.

Aerial photographs, official documents, witness accounts and expert testimony tell a different story. With the world’s media and aid organisations kept well away from the fighting, the army launched a fierce barrage that began at the end of April and lasted about three weeks. The offensive ended Sri Lanka’s 26-year civil war with the Tamil Tigers, but innocent civilians paid the price.

Confidential United Nations documents acquired by The Times record nearly 7,000 civilian deaths in the no-fire zone up to the end of April. UN sources said that the toll then surged, with an average of 1,000 civilians killed each day until May 19, the day after Velupillai Prabhakaran, the leader of the Tamil Tigers, was killed. That figure concurs with the estimate made to The Times by Father Amalraj, a Roman Catholic priest who fled the no-fire zone on May 16 and is now interned with 200,000 other survivors in Manik Farm refugee camp. It would take the final toll above 20,000. “Higher,” a UN source told The Times. “Keep going.”

Some of the victims can be seen in the photograph above, which shows the destruction of the flimsy refugee camp. In the bottom right-hand corner, sand mounds show makeshift burial grounds. Other pictures show a more orderly military cemetery, believed to be for hundreds of rebel fighters. One photograph shows rebel gun emplacements next to the refugee camp.

Independent defence experts who analysed dozens of aerial photographs taken by The Times said that the arrangement of the army and rebel firing positions and the narrowness of the no-fire zone made it unlikely that Tiger mortar fire or artillery caused a significant number of deaths. “It looks more likely that the firing position has been located by the Sri Lankan Army and it has then been targeted with air-burst and ground-impact mortars,” said Charles Heyman, editor of the magazine Armed Forces of the UK.

On Wednesday, Sri Lanka was cleared of any wrongdoing by the UN Human Rights Council after winning the backing of countries including China, Egypt, India and Cuba.

A spokesman for the Sri Lankan High Commission in London said: “We reject all these allegations. Civilians have not been killed by government shelling at all. If civilians have been killed, then that is because of the actions of the LTTE [rebels] who were shooting and killing people when they tried to escape.”

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