Police stopped the bomber at a checkpoint in the Grand Market, which was packed with shoppers and pilgrims visiting the Imam Ali Mosque, before he detonated explosives strapped to his body.

The blast, which happened at 10.30am local time, tore through the checkpoint and damaged shops facing the shrine, but did not damage the sacred building.

Hospital sources said that of those killed, 22 were men, including five policemen, and four Iranian pilgrims were injured in the blast as well as children.

“Before I reached the checkpoint, only a few metres from the shrine, I heard a huge explosion. Something hit me on the head and I fell. I couldn’t hear for a while but I saw bodies and human flesh everywhere,” said Hassan, 51, from his hospital bed.

“Suddenly my cart and the cans and the people were flying through the air,” said Moussa Khadhan, a 37 year-old street vendor, who was nearby at the time.

After the blast, police swarmed into the ancient city to shut it down. No cars were allowed to enter, shops were closed and crowds were made to disperse. Volunteers helped clear away the carnage and wash the pools of blood away from the streets.

Television footage of the devastation showed the body of a child being laid besides other bloodied corpses on a patch of ground beside a hospital. The dead were marked and numbered with white labels on their foreheads for identification.

Al-Qaeda in Iraq has staged several suicide bomb attacks in a bid to draw Iraq’s majority Shias into a sectarian civil war with Sunni Arabs, although there was no immediate claim for today's attack.

The city of Najaf, which is 100 miles south of Baghdad, is a major pilgrim destination for Shia Muslims around the world, especially from neighbouring Iran. Many Shia Muslims believe that the mosque contains tomb of Prophet Muhammad’s son-in-law, Ali.

Compared to other parts of Iraq, Najaf has been relatively stable. However, in December 2004, the Imam Ali shrine was targeted by a suicide car bomber killed 52 and wounded at least 140.

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