Damascus, June 29: A video has been released on the internet that shows a Catholic priest and two other people being beheaded by Islamist militants in Syria.
However, the country's main opposition group has claimed the video was made by the Syrian government to discredit the rebels.
"We will carry out all the necessary checks to ascertain when and where this incident took place," the Syrian National Coalition said.
"If the investigation shows the video is a fake, the Syrian National Coalition and the rebel Supreme Military Command will arrest those responsible and bring them to justice," the group added.
Vatican Radio, Vatican news agency Fides and other Catholic media reported that Father Francois Murad was killed when rebels attacked a Franciscan convent in a village near the Turkish border in Syria's northwestern Idlib province.
Murad was reported to be among three handcuffed victims in the graphic video posted onto news and social media websites.
The video shows a number of masked gunmen gather around the victims before cutting their throats and slowly severing their heads and holding them up to the camera, which then pans to the bodies lying in a pool of blood.
The Syrian Center for Documentation said the gunmen in the video were members of the Al Qaeda associated al-Nusra Front, and that they were foreigners.
"They speak Arabic with a broken accent, saying that through this act, they are applying the law of God on earth," the website said.