The Syrian Observatory for Human Rights reported on Sunday that Daesh fighters had seized control of the town of al-Qaryatayn in Homs province, part of a wider counterattack by the militants as they resist a fierce offensive in eastern Syria.
There was no comment from the Syrian army on the report that Qaryatayn, 120 km (70 miles) northeast of Damascus, had fallen.
Syrian government forces recovered Qaryatayn from Daesh some six months ago. The Observatory said Daesh fighters had seized control of Qaryatayn in a surprise attack launched after its fighters had infiltrated the town.
Daesh has lost swathes of territory to the Russian-backed Syrian government and to US-backed Syrian militias that are waging separate campaigns against the militant group’s last major strongholds in Deir al-Zor province in eastern Syria.