Updated 11.50am

A SUICIDE BOMBER struck a tent filled with medical students eating lunch at a military hospital in Kabul Saturday, killing at least six people and wounding 23, Afghan officials said.

The blast, which thundered across the capital, came as the Taliban have stepped up attacks as part of a spring offensive against NATO, Afghan government installations and officials.

Afghan army and police stepped up patrols on the streets.

Taliban spokesman Zabiullah Mujahid claimed responsibility for the attack, saying it was targeting foreign trainers and Afghan doctors who work with them.

He claimed two bombers took part, but Defense Ministry spokesman General Mohammed Zaher Azimi spokesman said only one attacker was involved and only one blast was heard at the Mohammad Daud Khan military hospital.

The hospital is the largest in Kabul with 400 beds, and its grounds contain numerous buildings and small parks.

A NATO military official said no casualties were reported among the group of international trainers who assist at the hospital. The official could not be named because he was were not authorized to speak to the media.

Azimi said all the dead and wounded were civilians and university students.

He added that “tents are used because there is not enough space in the hospital. This area is used by university students for training and eating meals.”

There have been many reports in recent weeks that insurgents were planning suicide attacks and other acts of violence inside the capital.

Watch pictures from the scene on Tolo TV here:

- additonal reporting from AP