BEIRUT : Militants killed at least 90 Syrian regime fighters, civilian security guards and employees when they seized a gas field in Homs province, a monitoring group said on Friday.The Syrian Observatory for Human Rights described Thursday’s takeover of the Shaar field as “the biggest” anti-regime operation by the Islamic State (IS) since it emerged in the Syrian conflict last year.“At least 90 people, mainly security guards and members of the (paramilitary) National Defence Forces, died in the IS attack on the Shaar gas field in Homs province,” Observatory director Rami Abdel Rahman said.“Twenty-five of the killed were civilian employees,” he told AFP. “The rest were security guards deployed by the oil ministry and members of the National Defence Force.”Gruesome footage apparently recorded by the militants at the gas field and distributed via YouTube showed dozens of bodies, some of them mutilated, strewn across the desert landscape.One video shows a militant posing with the bodies as he speaks in German interspersed with religious terms in Arabic, seemingly celebrating the killings. Abdel Rahman condemned the killings. “The Observatory condemns summary execution as a war crime, regardless of which side it is committed by in the Syrian conflict,” he said. “Summary execution is a war crime - whether of civilians or combatants. They are prisoners of war and must not be executed.”The Islamic State, which proclaimed a “caliphate” straddling Syria and Iraq last month, has also taken over Syria’s oil-rich Deir Ezzor province.Deir Ezzor borders Homs province as well as Iraq, where the militant group has spearheaded a major Sunni militant offensive that has seen large swathes of territory fall out of the Baghdad government’s control.