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.