Islamic State won territory from Syrian government forces in the eastern city of Deir al-Zor on Tuesday, its first gain there in about two months, a group that tracks the civil war reported.
Fighters from both sides were killed during the clashes in Deir al-Zor city, about 450 km (280 miles) northeast of Damascus in a province bordering Iraq, the Syrian Observatory for Human Rights said without giving a death toll.
Islamic State, which is being targeted by US-led air strikes in Iraq and Syria, seized large areas of Deir al-Zor's industrial region, meaning it now controls more than half the city, said Rami Abdulrahman, who runs the Observatory.
The Islamist militant group, which is also battling Kurdish forces for control of the town of Kobani at the Turkish border, brought reinforcements to Deir al-Zor in recent days, Abdulrahman said.
The US air force dropped arms to Kurds defending Kobani, also known as Ayn al-Arab, on Monday. Washington has ruled out such cooperation with the government of Syria's President Bashar al-Assad.
