Scores of people died in fierce overnight fighting Wednesday as Yemeni government forces battled tribesmen for control of the capital city of Sanaa.
Republican Guard shelling and pre-dawn street battles reportedly lasted until 5 a.m. and left at least 41 people dead. The tank shelling and gun battles broke out after tribal fighters seized control of northern parts of Sanaa. Forces loyal to Saleh remain in control of the southern part of the city, protecting key facilities.
Meanwhile, Islamist fighters loyal to al-Qaida seized the southern town of Zinjibar, raising concerns about the consequences of a collapse of government authority in Yemen.
Witnesses in Sanaa told The Associated Press that Presidential Guard units shelled the headquarters of an army brigade responsible for guarding sensitive government institutions. Army officers who have defected to the opposition say the government suspected the brigade commander was about to join forces with the movement to oust Saleh.
Opposition army officers, speaking on condition of anonymity in line with army rules, said the armored brigade commander, Brigadier-General Mohammed Khalil, was neutral and without political affiliation but had apparently angered Saleh.
The 41 dead included combatants from both sides of the conflict, said the medical officials, who spoke on condition of anonymity for fear of reprisals.
A resident who lives close to the fighting and would only give his first name, Zaher, told the AP that columns of smoke and fire billowed from Khalil's brigade headquarters and explosions could be heard.
Several ambulances were seen ferrying injured people to the al-Gomhuria General hospital, Zaher said.
The fighting followed the breakdown of a truce that had been declared Friday, after dozens of tribal fighters died in previous clashes.
Fierce clashes in the southern city of Taiz have left scores more people dead in recent days.
Yemen's already weak government has been rocked by four months of protests. Saleh has refused to cede power despite carefully negotiated exit deals hammered out by other Persian Gulf countries.
NPR's Peter Kenyon reported from Cairo, Egypt, for this story, which contains material from The Associated Press.