Yemen's government said Thursday that 52 people were killed in a suicide car bombing and a subsequent attack by gunmen on the Defense Ministry in the capital, Sanaa.
A statement by the Supreme Security Commission, which is led by President Abd Rabbuh Mansur Hadi, said 167 people also have also been wounded in Thursday's attack, the deadliest in Sanaa in years.
The commission said the casualties included soldiers, staff at a military hospital inside the Defense Ministry's downtown complex and civilians. The Defense Ministry also said a relative of the president was among those killed.
No one claimed responsibility for the attack. But the U.S.-allied country has been grappling with a security threat by groups linked to Al-Qaeda, which have repeatedly attacked government officials and installations over the past two years.
On Friday, a report from the Yemen government stated that 12 militants, mostly Saudis, carried out the deadly attack, according to the Associated Press.
President Hadi later met with military commanders inside the devastated complex and ordered an investigation into the incident, military officials said.
The brazen morning attack underlined the ability of insurgents to strike at the heart of the government as they exploit the instability that has plagued the country for more than two years.
Yemen's Defence Minister Mohammed Nasser Ahmed was in Washington on Thursday for talks with US officials. American forces also have been training and arming Yemeni special forces, and exchanging intelligence with the central government.
The Defense Ministry had earlier said that the attack targeted its hospital and that most of the gunmen had been killed or wounded.
"The attackers have exploited some construction work there to carry out this criminal act ... the situation is under control," the ministry said in a statement on its website Thursday morning.
Witnesses said the explosion shook the compound in the old district of Sanaa, where the country's central bank is also located.
"The attack took place shortly after working hours started at the ministry, when a suicide bomber drove a car into the gate," the Defense Ministry sources said.
"The explosion was very violent, the whole place shook because of it, and plumes of smoke rose from the building," an employee who works in a nearby building told Reuters.
Ambulance sirens and gunshots were heard after the blast as soldiers exchanged fire with the gunmen — said to have been disguised in Yemeni army uniforms — who had stormed the compound.
The Yemeni Health Ministry appealed to citizens to donate blood to help save the wounded.
At least two sources inside the Defense Ministry said the attackers came in two vehicles. One was driven by a suicide bomber who attacked the gate of the compound, while armed men entered the compound in the second, the sources said. The ministry statement made no reference to a suicide attacker.
In a statement provided to Al Jazeera, State Department Spokesperson Marie Harf said the U.S. "condemned" the "senseless" killings.
"We stand with Yemen against this violence and remain firmly committed to supporting the Yemeni people as they seek to conclude the National Dialogue and move forward peacefully with Yemen's historic democratic transition," Harf said.
U.K. Foreign Secretary William Hague also condemned the Yemen attack.
"As the U.N. Security Council reiterated just last month, all those attempting to disrupt Yemen's political transition will face serious measures. In a region which has seen huge instability and violence, Yemen’s progress so far has been commendable and we must not allow this process to fail," he said.
Political violence is common in Yemen, where an interim government is grappling with southern secessionists, Al-Qaeda-linked groups and northern Houthi fighters, as well as severe economic problems inherited from longtime President Ali Abdullah Saleh, who was forced out of office in 2011.
Armed groups were emboldened by a decline in government control over the country during protests that eventually ousted Saleh. They seized several southern cities before being driven out in 2012.
Al-Qaeda gunmen have killed hundreds of Yemeni soldiers and members of the security forces in a series of attacks since an offensive, which the United States has supported with intelligence and drones, drove them out of their strongholds.
In July of last year, an Al-Qaeda suicide bomber wearing a Yemeni army uniform killed more than 90 people rehearsing for a military parade in Sanaa.
Yemen's defense minister, Maj. Gen. Muhammad Nasir Ahmad, escaped a car bomb on his motorcade in September 2012 that killed at least 12 other people.
Al Jazeera and wire services