Islamic State group jihadists have killed at least 49 members of Syrian government forces in 24 hours of fighting near the desert city of Palmyra, a monitor said on Friday.
They included 15 Syrian soldiers and allied fighters killed in a Friday morning ambush near the Mahr oil field, the Syrian Observatory for Human Rights said.
IS fighters launched simultaneous attacks on several government positions in the eastern desert of Homs province on Thursday, including areas near the Mahr and Shaar oil and gas fields.
It has seized government checkpoints, silos and the village of Jazal, northwest of Palmyra, in the ongoing assault, the Observatory said.
The fighting has brought IS forces to within four kilometres (two and half miles) of Palmyra, which government forces recaptured from the jihadists in March.
The Observatory said the army had brought in reinforcements and was carrying out air strikes against IS in a bid to retake lost territory.
IS once held several key towns in Homs province, including Palmyra with its ancient ruins.
It overran the town in May last year, and systematically destroyed temples and tower tombs at the town’s UNESCO World Heritage site, before being pushed out by government forces.
It is still present in parts of the east of the province, and has carried out hit-and-run attacks on government positions in recent months.
But Observatory director Rami Abdel Rahman said the current assault was the first to see IS seize territory since it was pushed out of most of the province.