GENEVA — The United Nations said on Friday that a new video from Syria circulating on the Internet that appears to show antigovernment fighters kicking and summarily executing a group of frightened captive soldiers or militiamen could, if verified, represent evidence of a war crime to prosecute the perpetrators.

The video, which first appeared on Thursday, generated widespread attention internationally and provoked debate among insurgents and their sympathizers inside Syria. The video also illustrated what rights activists called a distressing trend of atrocities committed by both sides in the 20-month-old conflict.

“It looks very likely that this is a war crime, another one,” Rupert Colville, a spokesman for Navi Pillay, the United Nations high commissioner for human rights, told journalists in Geneva, the commission’s headquarters.

United Nations investigators had already collected evidence of war crimes and crimes against humanity by government and rebel forces in Syria that could support prosecutions of those responsible by national or international tribunals, Mr. Colville said. The new video, assuming its authenticity were proved, could be part of that evidence, he said. “There should be no illusion that accountability will follow,” Mr. Colville said.