The United States military has raised its alert status in Yemen, following a deadly terror attack in the capital Sanaa.
A suicide bomber and gunmen wearing army uniforms attacked Yemen's defense ministry, killing 52 people including foreign medical staff, government sources said, according to Reuters.
It was the country's worst militant assault in 18 months.
According to the news agency, one attacker drove a car packed with explosives into the gate of the ministry's compound, then gunmen in another vehicle sped in and opened fire on soldiers and doctors and nurses working at a hospital inside.
The attack wounded 167 people, said the Yemeni government's security committee. Two German and two Vietnamese doctors, and one Indian and two Filipino nurses were among the dead, it added.
No one immediately claimed responsibility, but a Yemeni expert told Reuters the attacked bore the hallmarks of Al Qaeda-linked terrorists who have repeatedly attacked government officials and installations over the past two years.
Ministry staff were arriving for work when the suicide bomber struck, two sources inside the ministry said.
The massive blast shook the bustling Bab al-Yemen neighborhood on the edge of Sanaa's old city.
Medics and a defense ministry official said the gunmen pulled a Western doctor and a Filipino nurse into the hospital's courtyard and shot them in front of local staff.
The attackers also killed one of Yemeni President Abd-Rabbu Mansour Hadi's relatives who was visiting a patient in the site, the defense ministry said on its website.
Al-Qaeda in the Arabian Peninsula (AQAP) has stepped up its attacks against Yemeni security forces in recent years, though these attacks have been mainly in the lawless southern and eastern provinces where jihadist groups are active.
The Islamist network has taken advantage of the weakening of the central government in Sanaa since a popular uprising that toppled president Ali Abdullah Saleh in 2011.
In August, the United States closed down all its embassies in the Middle East for several days after U.S. intelligence intercepted a phone call between al-Wuhayshi and Al-Qaeda leader Ayman al-Zawahiri. During the phone call, al-Wuhayshi reportedly vowed to carry out an attack that would "change the face of history".