Al-Qaeda claimed responsibility for the attack, saying it was retaliation for US drone strikes that have killed dozens of the terror network's leaders.
The attack - the deadliest in Sanaa since May 2012 - marked an escalation in the terror network's battle to undermine the US-allied government and destabilise the impoverished Arab nation despite the drone strikes and a series of US-backed military offensive against it.
Military investigators described a two-stage operation, saying heavily armed militants wearing army uniforms first blew up a car packed with 500 kilograms of explosives near an entrance gate, then split into groups that swept through a military hospital and a laboratory, shooting at soldiers, doctors, nurses, doctors and patients.
The investigative committee led by Yemen's Chief of Staff Gen. Ahmed al-Ashwal, yesterday said militants shot the guards outside the gates of the military hospital, allowing the suicide bomber to drive the car inside, but a gunfight forced him to detonate his explosives before reaching his target. It said the 12 militants killed, included Saudis.
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The report also raised the death toll to 56 and said more than 200 people were wounded. The foreigners killed included two aid workers from Germany, two doctors from Vietnam, two nurses from the Philippines and a nurse from India, according to Yemen's Supreme Security Commission.
Other military officials said American security agents were helping with the investigations, but that could not be confirmed. All officials spoke on condition of anonymity because they were not allowed to brief reporters.
Yemeni commandos and other security forces besieged the militants before they could reach the ministry's main building, preventing them from going further than the ministry's entrance gate.
Yemeni security forces launched a manhunt in the capital to find the perpetrators, sparking gunbattles that killed five suspected militants and a Yemeni commando, officials said.
Al-Qaeda in the Arabian Peninsula, as the group is known, is the product of a merger by the group's Yemeni and Saudi branches after a crackdown in the powerful neighboring kingdom. Among its leaders is another Saudi, Ibrahim al-Asiri.