BEIRUT: Al-Qaeda offshoot the Islamic State of Iraq and Greater Syria (ISIS) expelled rival rebels from the eastern Syrian city of Deir al-Zor Monday, tightening its grip on the oil-producing province abutting territory it also controls in Iraq, activists said.
ISIS' hardline Sunni fighters have been advancing against rivals in Deir al-Zor province with the help of weapons it seized in a lightning offensive against Iraqi government forces across the border last month.
The fighting has centered largely on control of oilfields and towns along the Euphrates River and has killed hundreds of fighters since the start of the year.
ISIS expelled dozens of rival rebels from Deir al-Zor city, including Al-Qaeda's Syria branch, the Nusra Front, and Ahrar al-Sham, a hardline Islamist group, the Britain-based Syrian Observatory for Human Rights said.
"The Islamic State of Iraq and Greater Syria (ISIS) is now in control of the entire Deir al-Zor province apart from a few areas and the military airport that the government is in control of," Observatory director Rami Abdul-Rahman said.
Fighters from rival Islamist groups had either fled or pledged allegiance to ISIS, he said, adding that government forces loyal to Syrian President Bashar Assad still controlled about half of Deir al-Zor city.
ISIS also killed a local Nusra Front leader, Abdul-Rahman added. Supporters of ISIS posted what it said were pictures of the Nusra leader's body online, but they could not be verified.
Omar Abu Leila, a spokesman for the rebel Free Syrian Army in the east, said hundreds of fighters had fled to the Deraa area in the south near Jordan and the Qalamoun region near Lebanon since ISIS declared a "caliphate" in the area it controls spanning eastern Syria and northern Iraq.
He said the influx of weapons from Iraq had tipped the balance in ISIS' favor and helped them secure control of local oilfields. "We have had no help from outside," Abu Leila said.