"Prabhakaran's son could have been killed in crossfire while he was in a little bunker. There is no need for an international probe. The photos are morphed," Prasad Kariyawasam told CNN-IBN.
A section of the media carried photographs of 12-year-old Balachandran Prabhakaran seated in a Sri Lankan army bunker just before he was killed allegedly at close range.
The pictures are part of a film, "No Fire Zone", which seeks to document the rights abuses during the final phase of Sri Lanka's war when the military crushed the Tamil Tigers in May 2009.
Kariyawasam urged Indian Tamil leaders to visit Sri Lanka "to see progress. Sentiment in Tamil Nadu is worrying. We cannot tell India how to vote in Geneva. It is a responsible regional power".
The reference is to next month's meeting in Geneva of the UN Human Rights Council where the US is expected to bring a resolution critical of Sri Lanka vis-a-vis human rights.
India voted with the US and against Sri Lanka last year.
Tamil Nadu Chief Minister J. Jayalalithaa, meanwhile, described as "a war crime" the alleged cold-blooded killing of Prabhakaran's son.
"The killing of Balachandran (Prabhakaran) is a war crime," the chief minister told the media here, and urged India to work with the US to pass a resolution in the UN denouncing rights violations in Sri Lanka.
Sri Lanka has denied that Prabhakaran's son was killed in cold blood, and maintained that he died in crossfire with the Liberation Tigers of Tamil Eelam (LTTE).
The chief minister said the young boy's killing was "unforgivable".
"I call upon the Indian government to hold discussions with the US and other like-minded nations and prepare a resolution to be passed by the UN (against Sri Lanka)," she said.
She added that in line with a resolution passed by the Tamil Nadu assembly, India should impose an economic embargo on Sri Lanka "with the cooperation of other countries".
The embargo should remain in place "until the Tamils who have been displaced there and confined in camps (after the conflict) are allowed to return to their homes and live with equal rights on par with" members of the majority Sinhalese community and "live a life of dignity".
The DMK also asked the Indian government to support a US backed resolution against the island nation at the United Nations Human Rights Council meet at Geneva in March.
Party chief M Karunanidhi, responding to the alleged cold-blooded killing of slain LTTE chief V Prabhakaran's 12 year-old son Balachandran, said this was proof enough that "(Sri Lankan President) Rajapakse is a war-criminal."
"Countries need not search for more proof that Rajapakse is a war criminal as the atrocity like gunning down of Balachandran cannot be seen anywhere else. There is no record of such a brutal murder in any country," he said in a statement.
He said images in UK-based Channel 4 documentary had moved political leaders in the state to tears. "How can one point a gun at the teenager?" he asked. "Channel 4 is making clear to the world various atrocities committed by the Sri Lankan Army and the face of Rajapakse, who claims himself to be a noble man, is exposed," he said.
The island nation's army had been spreading lies that the boy was killed in battle, he said.