Sri Lanka on Thursday rejected as "baseless and unacceptable" a new documentary by Britain's Channel 4 suggesting the army executed the 12-year-old son of a guerrilla leader after he surrendered.
The British news channel broadcast an account from a forensic expert on Wednesday night who said that the son of Sri Lanka's slain ethnic Tamil rebel leader Velupillai Prabhakaran appeared to have been shot at close range.
"Sri Lanka's Killing Fields: War Crimes Unpunished" also claimed it had "damning new evidence" of abuses against civilians.
"The ministry categorically rejects the video as baseless and unacceptable," the defence ministry said adding that Channel 4 had aired the documentary to defame Sri Lanka during a session of the UN Human Rights Council in Geneva.
In June, Channel 4 aired a documentary containing videos which it said amounted to evidence of war crimes by Sri Lankan soldiers during their final offensive against the Liberation Tigers of Tamil Eelam (LTTE) in 2009.
Prabhakaran, the head of the LTTE, was killed at the end of an army offensive against the brutal rebel group which ended a 37-year-old separatist war estimated to have cost up to 100,000 lives.
Human rights organisations have said that up to 40,000 civilians perished in the final months of fighting in 2009 during which the Sri Lankan army is accused of shelling populated areas as well as hospitals and refugee camps.
The government's own probe last year acknowledged that civilians had been killed, but said it was not due to any action by the security forces.
State Department spokeswoman Victoria Nuland said the US could not authenticate the Channel 4 video, but added: "As we stated many, many times, we are deeply concerned about allegations of international human rights law and human rights violations in Sri Lanka."