"The 15 students 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 schoolchildren have been kidnapped in Abia state. It is quite unfortunate."

Local media reported a ransom demand of 20 million naira, and the children's whereabouts are 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 an offshore 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.