Yemen said on Friday it had regained full control of its Defence Ministry compound in Sanaa a day after a militant attack, claimed by an al Qaeda-affiliated group, killed 56 people, including foreign medical staff.

The Yemeni military's chief of the general staff said in a preliminary report submitted to President Abd-Rabbu Mansour Hadi on Friday that an estimated 12 attackers, mostly Saudi nationals, had taken part in the assault and were all killed.

The report, seen by Reuters, said gunmen wearing army uniforms opened fire at soldiers guarding one of the hospitals inside the military compound. An explosives-laden pickup truck was then blown up.

"The terrorists were estimated at 12 and most of them were Saudi nationals. The (investigation) committee is still working on acquiring more information about the terrorists and their goals," the report said.

Among the dead were medics from Germany, Vietnam, India and the Philippines, and 215 people were wounded, according to the latest government figures.

It was the worst such attack in 18 months, heightening international concerns about threats emanating from a state that shares a long border with Saudi Arabia, the world's top oil exporter, and flanks international shipping lanes.

The interim Yemeni government is fighting southern secessionists and northern rebels in addition to al Qaeda-linked militants, who are seeking to overthrow the government and impose their version of Islamic law.

Responsibility for the attack was claimed by Ansar al-Sharia (Partisans of Islamic Law), an offshoot of al Qaeda in the Arabian Peninsula (AQAP), based in Yemen and among the most active and strongest arms of the global jihadi network.

"As part of the policy of targeting the operation rooms of pilotless planes, the mujahideen (holy fighters) have heavily struck one of these rooms in Defence Ministry headquarters," Ansar al-Sharia said on Twitter on Friday.

"Such joint military locations, which participate with the Americans in their war against this Muslim nation, are a legitimate target for our operations," another Twitter post read.

The US military raised its alert status in the region after the co-ordinated strikes on the ministry.

Murad Batal al-Shishani, a London-based analyst of Islamist groups, said the attack was likely to strengthen American-Yemeni cooperation against security threats.

"I don't know about the (US) drone programme (targeting militants), if this will escalate it or not. But generally, this will not affect the relationship. It will give them more reason to co-operate," he said.

Shishani said Thursday's attack, which combined a suicide bombing with a shooting spree, looked like an attempt "to copycat the Mumbai-style attack", referring to a 2008 assault in the Indian city that killed nearly 200 people.

He said it also echoed Islamist militant attacks this year on a desert natural gas plant in Algeria and the Westgate shopping centre in Nairobi, Kenya.

"They're resorting to this sort of tactic because it gains more media coverage, and it shakes the trust of the normal people in the security agencies. They say, 'You see, it's easy to attack and we have done that.' That is the message they are trying to send," said Shishani.

Yemen is also grappling with severe economic problems inherited from former president Ali Abdullah Saleh, who was forced out of office by a popular uprising in 2011.

Islamist insurgents took advantage of the chaos of Saleh's overthrow to seize several southern cities but were driven out in 2012 in a government offensive aided by US drone strikes.

AQAP militants have since killed hundreds of Yemeni soldiers and members of the security forces in a series of attacks, particularly in southern provinces.

In July 2012, a suicide bomber wearing a Yemeni army uniform killed more than 90 people rehearsing for a military parade in the capital. AQAP later claimed responsibility.-Reuters