More than 100 children have died of lead poisoning in Nigeria in recent weeks, health officials say.

The number has been rising since March, when residents started digging illegally for gold in areas with high concentrations of lead.

The victims were from several remote villages in the northern state of Zamfara.

A total of 163 out of 355 cases of poisoning have proved fatal, a Nigerian health ministry official told Reuters.

Dr Henry Akpan, the health ministry's chief epidemiologist, said:" [The victims] were digging for gold, but the areas also have large concentrations oflead."

Health authorities have set up two camps in the area to treat people who are suffering symptoms oflead poisoning.

The deaths were discovered during the country's annual immunisation programme, when officials realised there were virtually no children in several remote villages in the northern state, says the BBC's Abdulla! Kaura Abubakar in Kaduna.