London/Colombo: Pressure mounted on Sri Lanka over its rights record as a British channel broadcast a documentary suggesting that slain LTTE chief V Prabhakaran's 12-year-old son was killed by Army after the boy surrendered, prompting Colombo to reject it as "baseless and unacceptable".

The new documentary by a British Television Channel, which accused Sri Lanka of war crimes during the final battle with the LTTE, provided a forensic expert opinion claiming that Prabakaran's son had been executed at close range upon surrender towards the end of the war in 2009.

The programme titled 'Sri Lanka Killing Fields – War Crimes Unpunished' was aired in the UK on Wednesday night.

"We have obtained a sworn affidavit from a senior Sri Lankan officer in which he suggests that the boy was apparently interrogated about his father's whereabouts, and then killed," a Channel 4 spokeswoman said.

"Evidence that the shooting of the 12-year-old was an execution rather than a combat injury can be seen in high resolution photographs of his dead body - these stills are examined by respected forensic pathologist Derrick Pounder in the film."

Pounder describes the killing as homicide. “This is a murder - there's no doubt about it," he said.

Pounder said the boy, Balachandran Prabhakaran, had five dead males alongside him "who may well have been killed before he was killed".

"We have no evidence that he was blindfolded and he's been shot by someone standing in front of him with the end of the gun within a few feet of his body," he said.