BEIRUT: Fighters from Al-Qaeda's Nusra Front withdrew from two towns in eastern Syria Thursday, leaving most of the border province of Deir al-Zor under the control of advancing forces of the Islamic State of Iraq and Greater Syria (ISIS), the Syrian Observatory for Human Rights said.
It said that the Nusra Front pulled out of Mayadin and Shuhail, the group's regional stronghold, while local tribal fighters had pledged allegiance to ISIS, which has also swept through Sunni Muslim provinces in Iraq.
The Observatory, a British-based monitoring group, said that ISIS now controls an area of Syria five times the size of neighboring Lebanon.
In Deir al-Zor province only the regional capital and airport - still held by President Bashar Assad's forces - and a few villages remain outside the ISIS' control, it said.
Earlier this week ISIS seized the town of Al-Bukamal on the Iraqi frontier from the Nusra Front, securing both sides of the border crossing.
"For the first time ISIS has taken control over territory extending from the strategic town of Al-Bukamal on the Iraqi-Syrian border to the north-eastern edge of Aleppo," it said. Al-Bukamal is around 400 km from Aleppo.
ISIS fighters seized control of several Iraqi towns in a lightning offensive in June. The group says that it is restoring an Islamic caliphate on the cross-border territory it now controls and has called on Muslims to join it in jihad.