LAGOS - Gunmen have hijacked a school bus in Nigeria's Abia state, on the fringes of the oil-producing Niger Delta, and kidnapped 15 youngsters, police said yesterday.

The incident occurred early on Monday while the nursery and primary pupils were being driven to the Abayi International School in the southern state's commercial capital, Abia state police spokesperson Geoffrey Ogbonna said.

"The 15 children were being conveyed to school by the driver and the teacher that normally accompanies them when they were abducted," Ogbonna said.

"The kidnappers are demanding a ransom from the proprietress of the school. This is the first time school children have been kidnapped in Abia state. It is quite unfortunate."

Local media reported a ransom demand of about R1million. The children's whereabouts are still unknown.

Kidnapping of foreign oil workers and Nigerian civilians is relatively commonplace in the delta, which has been riven for years by militias demanding a bigger share from central government of the oil wealth that flows from beneath its soil.

However, the seizure of children is a worrying departure by the criminal gangs that also roam the region.

An amnesty that came into effect in the delta last year has reduced the overall levels of violence that curbed the output of Africa's largest crude oil producer.

However, three French oil workers were abducted in a raid offshore on a drilling ship last week.

Africa's most populous nation faces presidential and parliamentary elections early next year.

Historically, the run-up to polls has been marked by an increase in crime and security-related incidents.