Assad's army, Islamic State clash near Deir Al Zor's airport: monitor

Deir al-Zor airport is one of the last key strategic locations in the province out of the control of Islamic State, which has also seized swathes of territory across the border in northern and western Iraq.

The Syrian army responded by bombing areas around the airport, which supplies its forces in the east of the country, the British-based Syrian Observatory for Human Rights said. There were no details of casualties.

The fighting was just a few hundred meters from the airport, the Observatory's director Rami Abdurrahman said, adding that it would be tough for Islamic State to overcome government forces there.

Islamic State expelled rival rebels from Deir al-Zor city on Monday, tightening its hold on the oil-producing province bordering Iraq.

Capturing parts of the province has helped Islamic State link up territorial gains across Syria and Iraq, where it overran the northern city of Mosul in June. Last month it also declared an Islamic caliphate in territory it controls in both countries.

The group, previously known as the Islamic State in Iraq and the Levant, has made rapid gains in Syria in recent weeks, mostly by capturing territory from rival rebel groups.

There have also been confrontations with the Syrian army which has been bombing Islamic State positions more frequently, according to activists.

The Sunni Muslim militant group follows al Qaeda's hard-line ideology but draws strength from foreign fighters, many with experience in Iraq.

On Thursday it seized a gas field in eastern Syria and killed at least 90 people in one of its deadliest clashes with forces loyal to President Bashar al-Assad.