Afghan security forces were on guard near the military hospital compound in Kabul after the bombing [Al Jazeera]

At least six people have been killed and 23 injured in a suicide bombing at a surgery training session in a military hospital in the Afghan capital, Kabul.

The Afghan defence ministry said a lone bomber was responsible for the attack on Saturday, after reports that a second bomber was still at large on hospital grounds.

The bomber struck at 12:30pm local time (0900 GMT) in the cafeteria of the hospital where medical students were eating lunch, Mohammad Zahir, head of the police crime investigation unit, said.

He added that the dead were students.

The Taliban later claimed responsibility for the attack. Taliban spokesman Zabihullah Mujahid said in an emailed statement that the group had sent two suicide bombers into the hospital and killed many.

The Taliban vowed last month to carry out attacks, including suicide bombings, on foreign and Afghan troops and government officials.

Fear of attack

A doctor working inside the hospital told Al Jazeera that colleagues and patients rushed away from the direction of the blast and locked themselves in rooms, fearing another bomber would attack.

Nervous army and police troops herded a crowd far back from the walls of the hospital compound shortly after the explosion, our correspondent Sue Turton said, reporting from Kabul.

Witness Mohammad Hakim, who has a cart selling fruit, was nearby when the blast struck.

"It was a big explosion, I fell to the ground," the AFP news agency quoted him as saying. "The police arrived late at the scene, half an hour after the explosion took place."

The hospital is located just a few hundred metres from the United States embassy in what is known as the capital's "Green Zone."

"It's very interesting how the suicide [bomber] managed to get inside," our correspondent said.

Anyone wishing to visit family or friends in the hospital, which treats wounded soldiers, is required to go through a security check and obtain special identification cards, our correspondent said.

"It does seem that [the bomber] might have possibly had ... an ID," or might have been wearing a uniform, Turton said.

Source: Al Jazeera and agencies