Islamic State jihadists murdered a group of pro-government fighters in Syria yesterday, beheading some and shooting one with a rocket-propelled grenade, after seizing the ancient city of Palmyra and its world-famous Greco-Roman ruins. Revenge killings began almost immediately.A picture sent by activists to a Western journalist showed a row of men in a street in Palmyra, known locally by its Arabic name Tadmur, lying in a pool of blood. At least four had been decapitated.Other activists said that the dead men were members of the Shaitat tribe, anti-IS Sunnis from eastern Syria.The Shaitat suffered one of the worst IS massacres yet when they rose up against the jihadists' conquest of eastern Syria last year.When IS managed to reassert its authority it carried out a swathe of punishment killings, shooting, beheading and crucifying about 700 people.In a separate report, the citizen-journalist group Raqqa is Being Slaughtered Silently said IS had murdered another member of the Shaitat tribe, from Abu Hamam town, in Deir Ez-zour province, with a rocket-propelled grenade.The jihadists were shown cheering as one of the men lectures a young man tied to a pole then retreats and fires a bazooka.They then kick the body of the man, named as Ibrahim Shraideh.Troops loyal to Syrian President Bashar al-Assad fled Palmyra on Wednesday night in the face of a concerted IS attack that had led to hand-to-hand fighting earlier in the day.Activists claimed that government soldiers had been abandoned by their senior officers.The IS victory has cut off regime troops fighting in the city of Deir Ez-zour to the east.One of Palmyra's most prominent ruins is the Temple of Baal, which would be regarded by IS as idolatrous and thus a prime target for destruction. ..