The British government on Wednesday pressed Sri Lanka to investigate allegations of atrocities committed during the final stage of its civil war, after Britain's Channel 4 aired new footage of alleged war crimes.

British Foreign Office Minister Alistair Burt said a failure to probe the allegations at the end of the 25-year war with Tamil Tiger rebels could lead to international action against Colombo.

Burt said he was shocked by the “horrific scenes” contained in “Sri Lanka's Killing Fields” documentary aired late Tuesday. The video contained footage of what appeared to be the execution of prisoners by government troops.

Burt said Britain had been calling for a thorough, independent probe into claims of war crimes since the conflict ended in May 2009. He stressed that the whole of the international community will expect the Sri Lankans to give a serious and full response to the existing, convincing evidence.

But Sri Lanka's authorities say the video was fabricated and deny charges that the government violated human rights and humanitarian law. The government has accused the U.N. and the international community of being duped by a “disinformation” campaign orchestrated by the remnants of the Tamil Tigers.

More than 7,000 civilians are believed to have died during the Sri Lankan army's final offensive against the Tamil Tigers. At least 80,000 civilians are estimated to have been killed during the conflict that began in 1983.