A cluster bomb unit. – File Photo by AP

NEW DELHI: A report from a UN mine removal expert says unexploded cluster munitions have been found in northern Sri Lanka, appearing to confirm, for the first time, that the weapons were used in that country's long civil war.

The revelation is likely to increase calls for an international investigation into possible war crimes stemming from the bloody final months of fighting in the quarter-century civil war that ended in May 2009. The government has repeatedly denied reports it used cluster munitions during the final months of fighting.

Cluster munitions are packed with small ''bomblets'' that scatter indiscriminately and often harm civilians. Those that fail to detonate often kill civilians long after fighting ends.

They are banned under an international treaty adopted by more than 60 nations that took effect in August 2010, after the Sri Lankan war. The nations that haven't adopted the treaty include Sri Lanka, China, Russia, India, Pakistan and the US, which says the bombs are a valid weapon of war when used properly.

The Associated Press obtained a copy Thursday of an email written by a UN land mine expert that said unexploded cluster bomblets were discovered in the Puthukudiyiruppu area of northern Sri Lanka, where a boy was killed last month and his sister injured as they tried to pry apart an explosive device they had found to sell for scrap metal.

The email was written by Allan Poston, the technical adviser for the UN Development Program's mine action group in Sri Lanka.

''After reviewing additional photographs from the investigation teams, I have determined that there are cluster sub-munitions in the area where the children were collecting scrap metal and in the house where the accident occurred. This is the first time that there has been confirmed unexploded sub-munitions found in Sri Lanka,'' the email said.

During the final weeks of the war, tens of thousands of civilians and Tamil Tiger rebel fighters were trapped in a tiny section of Puthukudiyiruppu as attacking government forces closed in on them.

Lakshman Hulugalla, a Sri Lankan government spokesman on security matters, said the military had not used cluster munitions in the war against the Liberation Tigers of Tamil Eelam.

''We are denying that information,'' he said.

The UN did not immediately respond to an AP request for comment.

Alan Keenan, Sri Lanka project director for the International Crisis Group, said the revelation ''makes more clear than ever the need for a thorough and independent investigation of alleged violations of the laws of war by both the government and the LTTE, which only an international body can provide.''

Poston's email, dated Tuesday, said mine clearers in Sri Lanka had not been prepared to deal with the bomblets, and are now relying on the experience of deminers who had worked in Lebanon, where Israel used cluster munitions in its 2006 war.

One deminer with experience in Lebanon was asked to clear the area and train other teams in how to handle the bomblets, according to the email. The local mine clearing office is adopting the Lebanon standards, and Unicef was informed of the need to educate the local population about the dangers of the unexploded munitions, it said.

The army's demining unit also was informed of the discovery, the email said.

''Cluster sub-munitions are extremely dangerous items of (unexploded ordnance) and can explode with the slightest movement or touch,'' the email warned.

UN officials first reported the use of cluster munitions in the conflict zone in February 2009, saying they appeared to hit in an area around a hospital that was pounded by artillery fire for more than 16 hours. The government denied possessing the weapons and the UN said it accepted that denial.

A report last year by a UN panel of experts found credible allegations of war crimes by both Sri Lankan government forces and the rebels. The experts said there were unconfirmed reports the army had used cluster bombs against civilians in a No Fire Zone the government had set up.

Witnesses reported hearing large explosions followed by multiple small explosions that would be consistent with such munitions. The expert panel said some injuries were also consistent with cluster munitions, and called for further investigation of the issue.

A New York-based human rights group said it would have been disastrous to use such weapons among the hundreds of thousands of civilians crowded into the Sri Lankan war zone.

''If there is evidence that cluster weapons were used, it would show yet again, the government's constant attempts at deception and underscore our demand that there should be an independent international investigation into all allegations of laws-of-war violations,'' said Meenakshi Ganguly, South Asia director for Human Rights Watch.