A video published on Thursday, May 16 showed fighters of the al Qaeda-linked Nusra Front in Syria executing 11 men they accused of taking part in massacres by President Bashar al-Assad's forces, according to Reuters.

The film is believed to be from eastern Deir al-Zor province and dates from some time in 2012, according to the Syrian Observatory for Human Rights, an opposition monitoring group.

The Observatory's head, Rami Abdelrahman, said the Nusra Front has recently been releasing several videos of their past operations. He said the man seen executing the prisoners in the video - a Nusra commander - had been killed in March 2013 in battles with local tribes in the province.

The footage shows the commander, his face covered in a black balaclava, shooting each prisoner in the back of the head as they kneeled, blindfolded and lined up in a row in the sand.

Videos of executions and torture have become increasingly common in Syria, where more than 94,000 people have been killed in a conflict now in its third year, according to the British-based Observatory, which has a network of activists in Syria.

Such videos posted online are hard to verify due to government restrictions on access for independent media. The Nusra video is the second video to be published in the past two days showing executions by fighters who say they are from al Qaeda-linked groups.