BEIRUT — Extremists killed at least 115 Syrian troops, guards, and workers as they captured a gas field in central Syria following daylong clashes, activists said Friday.
More than 20 militants also died in the fighting on Thursday for the Shaer gas field, the deadliest battles so far between fighters of the Islamic State group and forces loyal to President Bashar Assad.
Fighters from the Islamic State have in the past few weeks seized a huge chunk of territory straddling the Iraq-Syria border where they declared a self-styled caliphate. Earlier, they captured much of Syria’s oil-rich eastern province of Deir el-Zour.
The massive assault on the Shaer field, in the desert region of Palmyra in the central province of Homs, began with a suicide bombing and an attack on checkpoints on Thursday, said an activist there who goes by the name Beibares Tellawi.
The militants seized the field after fierce clashes with government forces that went on for 12 hours, Tellawi said.
‘‘This is the biggest operation [by Islamic State fighters] against the regime in Homs province,’’ Tellawi said, speaking via Skype from Homs.
The Britain-based Syrian Observatory for Human Rights said 115 people on the government side were killed.
The Observatory said 21 Islamic State fighters were killed. Tellawi put the figure at 27.
An official in the Homs governor’s office 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 fate of about 200 people captured is still unknown.
A video said to be from the area and released by activists shows bodies strewn across a desert area. It also shows jihadis with two multiple rocket launchers and two tanks, which they claim were seized.