Syrian rebels pressed their lightning advance on Saturday, saying they had seized most of the south, as government forces dug in to defend the key central city of Homs to try to save President Bashar Assad's 24-year rule.

Since the rebels' sweep into Aleppo a week ago, government defences have crumbled across the country at dizzying speed as insurgents seized a string of major cities and rose up in places where the rebellion had long seemed over.

Besides capturing Aleppo in the north, Hama in the center and Deir al-Zor in the east, rebels said they have taken southern Quneitra, Deraa and Suweida and advanced to within 50 kilometers of the capital.