A reporter at the scene said three areas in north Sanaa had been hit by heavy shelling and gunfire between government troops and armed followers of a powerful tribal leader, Sadeq al-Ahmar, who supports the opposition.

Many residents fled their homes as the fighting intensified, shattering three days of calm in the capital after Saleh ordered a ceasefire upon his surprise return to Yemen on September 30.

The truce had followed more than a week of fighting when over 100 people died, raising worries that the country could be dragged closer to civil war.

Saleh had been recuperating in Riyadh for three months after a bomb attack in June and had been pressured by Western diplomats to stay inSaudi Arabia while they struggled to push through a long-stalled power transition plan.

Ahmar's men battled state security forces on September 29 and troops from the elite Republican Guard, which is headed by Saleh's son. It remains unclear how the fighting began.

During the lull politicians and diplomats had scrambled to get back on track derailed negotiations on a plan brokered by Gulf Arab states under which Saleh would stand down.