The slaying of nearly 200 Yemeni soldiers by al-Qaeda militants in a brazen weekend attack poses the first major test to the country's newly elected president, who has vowed to crush the terror network and purge military commanders still loyal to his predecessor.

For the second successive day, tens of thousands protested in several cities across Yemen to demand that Abed Rabbo Mansour Hadi prosecute army commanders suspected of negligence or collaboration with al-Qaeda in the Sunday attack, which saw headless bodies of soldiers dumped in the desert in the deadliest defeat for the army in its nearly yearlong campaign against the militant movement in the south.

Protesters and military officials blame the defeat on commanders installed by ex-leader Ali Abdullah Saleh, who they say promoted his allies and relatives on the basis of loyalty not competence. They say these officers were lax about taking the fight to al-Qaeda, and may have struck local deals with the militants.

If Hadi leaves these commanders in place, military officials say, al-Qaeda is likely to expand areas under its control in the lawless south of the country or stage similarly bold attacks like Sunday's.

The slowly emerging grim details of the violence in the southern Abyan province and the magnitude of the army's defeat point to the heavy burden left squarely on Hadi's shoulders by more than three decades of Saleh's rule.

Surprise attack as soldiers slept

The military officials accounts of the disaster involved al-Qaeda militants sneaking across the desert to the back lines of Yemeni forces at dawn, when many of the troops were asleep in their tents.

The raiders sprayed the sleeping soldiers with bullets and later dumped their bodies, including some missing heads or mutilated, in the desert near Abyan's provincial capital of Zinjibar.

On Tuesday, military officials said the death toll among army troops has risen to 185. Another 55 soldiers were captured and paraded through a nearby town by the militants. The figure for al-Qaeda fighters killed in the fighting remained unchanged at 32.

Medical officials in the area confirmed the latest death toll and said some of the bodies of soldiers recovered were missing their heads and bore multiple stab wounds. They said that bodies packed the military hospital morgue to which they were taken, with some taken to vegetable freezers in a military compound for lack of space.

During his inaugural speech last month, President Hadi said his two top priorities were to restructure the armed forces and launch a national dialogue among various political factions.

Among his first decrees as president was to replace the military commander of the nation's southern region, Maj. Gen. Mahdi Maqoula, a Saleh loyalist privately accused by officers under his command to have hindered the arrival of vital supplies to army forces fighting al-Qaeda in the south.

The replacement came only days before Sunday's attack, raising suspicions about Maqoula's role in the al-Qaeda attack.

The surprise attack and the mutilations have left government troops "fearful" and suffering from "low morale," according to a senior military official who was a member of the defeated force.

The senior military official said the attack left soldiers "fearful of al-Qaeda because of the barbarism and brutality of their attack."

"Al-Qaeda managed to deal a blow to the army's morale. Imagine how soldiers feel when they see the bodies of their comrades dumped in the desert," he said.

The military officials had earlier said that militants overran the base and captured armoured vehicles and artillery pieces, which they turned on the army.

The senior official said the soldiers were taken unaware.

"It was a massacre and it came by surprise as the soldiers were asleep," he said. Militants sneaked behind army lines and attacked from the rear where there was "zero surveillance," he said.

'Coming days will be decisive'

Hadi took power last month from longtime ruler Saleh as part of power-transfer deal backed by the United States and initiated by Arab Gulf countries.

The yearlong uprising against Saleh had caused a deterioration of central state authority throughout the country, and allowed al-Qaeda to seize Zinjibar in May and fight off repeated army offensives to retake it. They captured the nearby town of Jaar last April.

The U.S. had hoped that replacing Saleh would take some pressure off of Yemen's government and military, who also confront tribal and separatist insurgencies, and allow them to fight back more effectively against the militants.

Maj. Gen. Salem Katton, who replaced Maqoula as commander of the southern region, told his troops on Tuesday that the battle with al-Qaeda has not started yet.

"The coming days will be decisive and will teach them a harsh lesson," he said.

But he may not yet have the means to do so: the military officials in Abyan said the forces routed by al-Qaeda were poorly equipped, and that better-trained, better-armed specialized anti-terrorist units needed to be brought to the front.

All officials spoke on condition of anonymity because of military protocol or because they were not allowed to speak to the media.