The prospect of a war crimes probe following Sri Lanka's military victory over Tamil Tiger rebels looms larger, with UN chief Ban Ki-moon backing growing calls for a full investigation.

 Thousands of civilians have been killed during the offensive against the Liberation Tigers of Tamil Eelam (LTTE). Sri Lanka's military declared final victory in the decades-old conflict on Monday after overrunning the rebels' last holdout in the northeast.
 

Both sides in the conflict have been accused of rights violations, with numerous aid agencies and rights groups alleging indiscriminate army shelling and condemning the Tigers for using civilians as a human shield.

UN officials say more than 6,500 Tamil civilians have died in the conflict since the start of the year, with the final days of the battle described as a "bloodbath on the beaches."

The UN secretary general, who is due to visit Sri Lanka at the end of the week, said that any serious allegations of war crimes "should be properly investigated."

The UN's Human Rights Council is to hold a special session on Sri Lanka next week.

"There has to be accountability for what has gone on in Sri Lanka, there has to be clarity and there cannot be impunity," Rupert Colville, a spokesman for UN High Commissioner for Human Rights, Navi Pillay, said last week.

Pillay said in March that both sides may be guilty of war crimes.

Former colonial power Britain also wants a probe, citing the "truly shocking and appalling" numbers of civilian dead.

British Prime Minister Gordon Brown had warned the Sri Lankan government that there would be "consequences for its actions."

According to Human Rights Watch, satellite imagery and witness accounts contradict government claims that heavy weapons have not been used. It said both sides in the war were using civilians as "cannon fodder."

Amnesty International has also demanded that "the mounting evidence of serious violations of international law" be investigated.