(CNN) -- Armed, masked men raise their weapons and shoot dead three men sitting on a curb in a Syrian city. The images are captured on video, purportedly showing Islamist rebels carrying out a public execution of soldiers.

The incident occurred in Raqqa city, in the north. Videos produced by locals sympathetic to the Islamists have appeared on the Web, and an opposition group, the Syrian Observatory for Human Rights issued a report on the incident Tuesday.

"Rebel fighters from the Islamic State of Iraq and Bilad al-Sham (Syria) have summarily executed three men in the middle of a square in Raqqa city," the Observatory said. "The jihadis stated that the detainees were officers from the Syrian army."

The videos show armed masked men standing in a street, with one of them reading from a paper. A crowd of onlookers can be seen in the background. Gunmen shoot dead three men who are sitting on a curb and the militants raise their weapons in celebration.