With shaggy hair and beard, and mumbling incoherently, Sher Mohammed, 40, lies curled up under the shade of a tree to which he has been chained for a month.

This is the standard "treatment" for mentally ill people who have been coming to the Mia Ali sanctuary in eastern Afghanistan for 300 years.

"Here, we don't give medication or advice, there is no other treatment than belief in God," says Mia Mohammad Naeem, one of the guardians of the shrine in Samar Khel village, 10 kilometres (six miles) from the city of Jalalabad.

"It's a spiritual treatment with the Koran and diet," he says.

At the Mia Ali sanctuary the patients, presumed to be possessed by jinns (demons), are chained by the wrist to a tree or in a concrete room, under shelter or in the open, for 40 days.

They are fed only bread and water and get no change of clothing.

In a shack close by, Ghulam Haider, 45, crouches on the ground, tirelessly writing in Arabic the different names of God and verses of the Koran on pieces of paper.

"Some of these taweez (amulets) will be poured in a glass of water and then drunk. Others will be burned or used as a necklace. Every single word of the holy Koran is healing," he says.