Islamic State (IS) militants have captured al-Qaryatain town, in the province of Homs, from pro-government forces, reports say.
The militants launched the attack with suicide bombings at the town’s checkpoints, according to the Syrian Observatory for Human Rights (SOHR), a UK-based monitoring group.
It said the capture of the town links IS-held Palmyra with the Qalamun area.
Separately, the US launched its first drone strike against IS from Turkey.
A Pentagon spokesman did not give any further details about the strike, which reportedly took place on Monday.
Turkey last month said it would allow US aircraft to use its southern Incirlik airbase to attack IS in Syria, potentially speeding up air strikes against the militants.
Al-Qaryatain was captured in the militants’ first major offensive since May, when they seized the historic town of Palmyra, famed for its Roman-style ruins.
The town is thought to have a mixed population of around 40,000 people, including Sunni Muslims and Christians, as well as thousands of people who have fled fighting elsewhere in the country.
According to the SOHR, the capture of the town could help IS move fighters and material between Palmyra and territory that it controls in Qalamun, to the west.
Scores of pro-government and IS fighters are said to have been killed in the battle for the town.
More than 230,000 Syrians have died in the civil war, which began after anti-government protests in March 2011.
Rebel groups that were originally fighting against the government of President Bashar al-Assad have also been battling each other in an increasingly complex and bloody conflict.