BEIRUT (AP) — A new video appears to show Syrian rebels killing a group of captured soldiers, spraying them with bullets as they lay on the ground. Human rights groups today warned that the gunmen may have committed a war crime.

The video raises concerns over the rebels just ahead of a major conference this weekend in Qatar at which the United States is trying to unify the opposition under a new leadership. Washington and its allies have been hesitant to give stronger support to the rebellion in part because of worries over its multiple divisions and lack of organization.

The killings took place Thursday during an assault by rebels on the northern town of Saraqeb, the scene of heavy fighting in past weeks between rebels and forces of President Bashar Assad’s regime, according to an antiregime activist organization, the Syrian Observatory for Human Rights.

Rebels are now in full control of Saraqeb after regime troops pulled back during Thursday’s fighting, the Observatory said. That gives the rebels a strategic point on the main highway linking Syria’s largest city Aleppo — which rebels have been trying to capture for months — with the regime stronghold of Latakia on the Mediterranean coast.

Human rights groups said they were trying to confirm the video’s authenticity. The footage was consistent with other Associated Press reporting in the area. The video is dated Thursday, a day when the Observatory reported heavy attacks by rebels on regime checkpoints at Saraqeb.

The amateur video, posted on YouTube, shows a crowd of gunmen, apparently rebels, in what appears to be a building under construction.

They surround a group of captured men on the ground, some on their bellies as if ordered to lay down, others sprawled as if wounded. Some of the men are in Syrian military uniforms. “These are Assad’s dogs,” one of the gunmen is heard saying of the captured men.

The gunmen kick and beat some of the men, who appear terrified as one gunman shouts, “Damn you.” The exact number of soldiers in the video is not clear, but there appear to be around 10 of them.

Seconds later, amid the screams of those captured, gunfire erupts for around 35 seconds and the men on the floor are seen shaking and twitching, apparently from being struck by bullets. The spray of bullets raises a cloud of dust from the ground.

The video is titled “prisoners and dead from the regime military at the Hmeisho checkpoint.” On Thursday, the Observatory had reported 12 soldiers killed at Hmeisho, outside Saraqeb.