The video, titled "Killing Fields" and released by a British TV station, showed soldiers allegedly killing unarmed rebels, according to foreign news agency reports.
Sri Lanka will Saturday celebrate four years since the end of the war and the defeat of the LTTE, but the government remains haunted by allegations of having committed human rights abuses during the final phase of the battle.
A Sri Lankan government statement quoted the Head of Mission of Sri Lanka to the European Union, P.M. Amza as requesting the British channel to provide original materials available with them to help the probe process.
Amza also alleged that the TV station has made serious mistakes by misinterpreting what the witnesses have said in Tamil on the video to suit the agenda of that station.
He also refuted allegations on the killing of a 12-year-old boy identified as the son of slain LTTE leader Velupillai Prabhakaran.
The government statement said the LTTE was not an ordinary group of terrorists but one in which all its cadres carried cyanide capsules to kill themselves if captured by the army.
"It was also a ruthless terrorist group which never hesitated to use even disabled and pregnant women as suicide bombers in order to achieve its ulterior objectives," the statement said.
The Sri Lankan government said it has taken efforts to rehabilitate around 12,000 former LTTE cadres including 594 child soldiers after the end of the conflict, who are now leading "peaceful and dignified lives".