Syria's army and allied militia fighters seized the only road into the rebel-held part of Aleppo on Sunday, tightening a siege around opposition areas of the northern city, which President Bashar Assad has pledged to recapture.

Aleppo has been a major battlefield of Syria's civil war since rebels swept into it in the summer of 2012, and an opposition defeat there would mark their biggest setback in five years of conflict.

Around 300,000 people live in rebel-held eastern Aleppo and for months their lifeline has been a highway leading north from the city known as the Castello Road.