Syrian troops and their Iran-backed allies "suddenly" pulled out of eastern Deir Ezzor city and its surroundings Friday, a war monitor said, as a rebel offensive dealt the government a series of stunning blows.

"Syrian regime forces and commanders of Iran-backed allied groups suddenly withdrew from Deir Ezzor city and its countryside with columns of soldiers heading towards central Syria," Rami Abdel Rahman, who heads the Syrian Observatory for Human Rights war monitor, told AFP.