At least 60 soldiers and pro-regime fighters were among the 270 killed in a bloody jihadist attack on a gas field in central Syria, a pro-regime newspaper reported on Sunday.
With the Syrian counter-attack to try to recapture the Shaar field in Homs province in its third day, Al-Watan, citing a military source, give a toll of "60 martyrs" among regime forces.
The Syrian Observatory for Human Rights had earlier reported it had documented "the deaths of 270 people killed in fighting or executed" by Islamic State (IS) militants.
"A large majority of the men killed were executed at gunpoint after being taken prisoner" in the seizure of the field, said Observatory chief Rami Abdel Rahman.
"Eleven of the dead were civilian employees, while the rest were security guards and National Defence Forces members," he added.
The Britain-based Observatory, which relies on a network of activists and medics on the ground, said at least 40 IS militants and 11 soldiers have been killed in the counter-attack, which was backed by aircraft.
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The Observatory also reported further "violent clashes... in and around the gas field" on Sunday.
Thursday's takeover of the Shaar field was the "biggest anti-regime operation by the IS" since the jihadist group rose to prominence last year among rebel groups in Syria's conflict, it said.
On Sunday, the Observatory said the IS had carried out another 24 executions at a Deir Ezzor oilfield in eastern Syria of men abducted during the past month.
At least eight of the men killed on Saturday night were fighters from other anti-regime rebel groups, it said.
The Observatory also reported 17 rebels killed in clashes with the IS near rebel-held Akhtarin, a town in the northern province of Aleppo.
And in Daraa province in the south, it said nine rebels were killed in clashes with regime forces.
IS jihadists proclaimed an Islamic "caliphate" straddling Syria and Iraq last month and have also taken over oil-rich Deir Ezzor province.
Deir Ezzor borders Homs province as well as Iraq, where the jihadist group has spearheaded a major Sunni militant offensive that has seen large swathes of territory fall out of Baghdad's control.