Sri Lanka is marking 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 last spring.

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 was high - an estimated 30,000 Tamils caught in the conflict zone perished in intense fighting in the finaly days of the war.

Though the Sri Lankan government dismisses the figures as exaggerated, 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.

Speaking to Al Jazeera, Louise Arbour, the president of the International Crisis Group said that clear evidence had emerged that suggested there was a case to answer.

"We are starting to get evidence that seriously challenges the narrative that the government of Sri Lanka has maintained all that time regarding the level of casualties and the methodology of war, demonstrating there were deliberate attacks on civilians, on humantarian institations and hospitals," she said.   

Sri Lanka's majority Sinhalese government has, however, rejected the allegations.

"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 I’m 100 per cent certain that the government did not use heavy artillery after that commitment," Palitha Kotha, Sri Lanka's foreign secretary during the war, said.

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 government-run internment camps where displaced Tamils are being held.

About 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 dries up.