A suicide bomber killed six students and wounded almost two dozen people at a heavily guarded national military hospital in Kabul on Saturday.
Mohammad Zahir, the head of the police crime investigation unit, told Reuters the bomber struck in the Charsad Bestar Hospital's cafeteria as medical students had gathered to eat lunch at 12:30 p.m. local time.
An Afghan intelligence official told the BBC that there were two suicide bombers at the hospital. One caused the blast in the cafeteria, and the other has not yet been found.
"As soon as the explosion took place, everyone started running from the cafeteria area," a doctor told the BBC. "It was at lunch-time. We have been locked inside our rooms and departments because the other attacker is still somewhere."
The Taliban claimed responsibility for the explosion. The Taliban are beginning their spring offensive, vowing to carry out attacks on foreign and Afghan troops as well as government officials.
The attack also comes a few weeks after U.S. forces killed Al Qaeda leader Osama bin Laden during a raid in Pakistan, prompting calls by Islamist extremists to retaliate.
The hospital, one of the country's best equipped, has 400 beds and is filled with foreign medics who trained Afghans, The New York Times reported.
The hospital is in one of Kabul's most heavily guarded areas, called Wazir Akbar Khan. It is located near the U.S. embassy as well as other foreign embassies and the offices of international organizations and NATO facilities.
The attack therefore adds to concerns of insurgent infiltrators in the ranks of Afghan forces.
As GlobalPost's Jean MacKenzie reported last month, the Taliban are publicly gloating that they have 150-200 infiltrators in Afghan institutions, just waiting to pull the cords on their suicide vests.