There were growing signs of disarray in beleaguered President Ali Abdullah Saleh's military. Fighting raged until 5 am local time, and witnesses said 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 armoured 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.
The fighting engulfed the Hassaba neighbourhood that contains the family compound of influential opposition tribal leader Sheik Sadeq al-Ahmar, and to the north of that district where Republican Guard units protect Saleh's former residence.
The units, led by one of Saleh's sons, and special forces wearing uniforms of government security troops attacked but failed to recapture the Hassaba administrative building from tribal gunmen.