Republican Guard shelling and pre-dawn street battles between government forces and rival tribal fighters killed at least 41 people in Yemen's capital Sanaa Wednesday.

There were growing signs of disarray in beleaguered President Ali Abdullah Saleh's military.

Fighting raged until 5 a.m., 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, Brig.-Gen. 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.

Collective punishment

On Tuesday, Saleh imposed collective punishment on the Hassaba neighbourhood by cutting water supplies and electricity.

A resident who lives close to the fighting and would only give his first name, Zaher, said 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.

Al-Ahmar tribesmen were seen Wednesday morning around the office of the prosecutor general in Shamlan neighbourhood, west of the capital. They were accompanied by two armoured vehicles from the 1st Armoured Division which defected to the opposition two months ago.

There also was fighting for the first time early Wednesday in the Hada neighborhood, a stronghold for Saleh supporters in the south of the capital. The Interior Ministry said in a statement that tribesmen had taken over a five-storey building there after clashing with the army.