Medical teams have been sent to remote villages hit by the earthquake in northern Afghanistan after reports of a sharp increase of disease among survivors.

Many are said to be suffering from an acute form of diarrhoea which can be life-threatening if not treated.

A BBC correspondent in the region says lack of food and water has aggravated the problem.

The international relief effort is being hampered by weather and transport difficulties -- only four helicopters are available.

Others which were promised have failed to arrive.