Sri Lanka has marked the first anniversary of the end its bloody civil war, which finished after government troops defeated the Liberation Tigers of Tamil Eelam (LTTE) in a final offensive against the rebel group.

The government declared final victory in the 25 year civil war with the killing of Velupillai Prabhakaran, the LTTE's leader and subsequent capture of the group's final stronghold.

But the cost in civilian life was high - an estimated 30,000 Tamils caught in the conflict zone perished in intense fighting leading up to the end of the war.

Access to the conflict zone has been restricted, and experts say they will never know exactly how many innocent people died in the offensive.

Sri Lanka's government says the figures have been exaggerated, but independent human rights groups say they have evidence that government forces fired on hospitals, food distribution points and groups of the civilians during the fighting and have called for an investigation into possible war crimes committed by both sides during the conflict.

These allegations are rejected by Sri Lanka's majority Sinhalese government.  

"The government, at the level of the president, gave an assurance to the community that heavy guns will not be used when the civilians were going to be relieved or were going to be rescued, and Im 100 per cent certain that the govt did not use heavy artillery after that commitment," said Palitha Kotha, Sri Lanka's foreign secretary during the war.

The international community has also been criticised for its lack of action during the conflict. Rights groups say that the UN and others turned a blind eye to the civilian cost of the campaign, and have criticised their involvement in the sprawling camps for people displaced by the fighting.

80,000 Tamils are still living in the camps, unable to rebuild their lives and coping with deteriorating conditions as money used to run the camps dwindles away.