"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 a news channel.
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.
Mr 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.