A United Nations campaign to vaccinate millions of children in Afghanistan against polio has begun amid reports of continued fighting.

UN officials said they had asked both the ruling Taleban and the opposition forces of commander Ahmad Shah Masood to agree to a ceasefire, but there are unconfirmed reports of renewed clashes in the north of the country.

The three-day nationwide programme aims to reach four million children under the age of five.

Polio is still widespread in Afghanistan which has one of the highest rates of child mortality from the disease.