Recently released victims of kidnapping in Nigeria say snakes were used to terrorise them into raising ransoms.

The West African country has seen a sharp rise in kidnappings, with ever greater sums being extorted.

One abductee told the government-owned News Agency of Nigeria some victims were forcibly taken to areas known to be snake-infested.

"That's when a victim will ask friends and family to sell everything to raise the ransom – house, cars, goods, just everything," the agency quoted an abductee as saying.

Local doctors have confirmed that some kidnap victims have required treatment for snake bites following their release.