Islamic militants killed about 100 Syrian troops, guards and workers as they captures a gas field in central Syria following daylong clashes, activists said Friday.
The attack was the deadliest fighting so far between fighters of the Islamic State group and forces loyal to President Bashar Assad.
The militants have in the past few weeks seized a huge chunk of territory straddling the Iraq-Syria border where they declared a self-styled caliphate, and have already captured much of Syria's oil-rich eastern province of Deir el-Zour.
The massive assault Thursday began with a suicide bombing and an attack on army checkpoints near the Shaer gas field in the desert region of Palmyra, according to an activist in the central province of Homs, who goes by the name Beibares Tellawi.
The militants seized the field after fierce clashes with government forces, Tellawi said.
The Britain-based Syrian Observatory for Human Rights said 115 people were killed. The Syrian government has not commented and an official in Homs contacted by The Associated Press said he had no information on the incident. The Syrian government rarely comments on deadly attacks targeting its forces.
The Observatory and Tellawi said the field fell to the militants Thursday night after a day of clashes. They both said that the fate of more than 200 people captured in the facility is still unknown.
The Observatory said 21 Islamic State fighters were killed during Thursday's battle, while Tellawi put the figure at 27.