GENEVA (AP) _ Two United Nations experts will arrive in northern Afghanistan this week to investigate a mysterious epidemic that so far has killed at least 150 people, the World Health Organization said Tuesday.

Some 2,000 cases of the disease have been reported in a mountainous area near the country's border with Tajikistan, WHO spokesman Gregory Hartl said.

``The cause of this disease is still unknown,'' he added. ``It seems to be a type of respiratory illness. We don't know.''

The figures are ``still incomplete'' as they reflect the number of cases from only five villages, Hartl said. The disease has been reported in at least 18 villages, most of them extremely remote.

The United Nations received the first reports of the epidemic earlier this month from local authorities in the village of Darwaz.