* Gunmen kidnap 15 Nigerian children
* Bus hijacked on way to school
* Media reports speak of ${esc.dollar}150,000 ransom demand
(Updates with another kidnapping, paragraph 9)
LAGOS, Sept 28 (Reuters) - Gunman have hijacked a school bus in Nigeria&${esc.hash}39;s Abia state, on the fringes of the oil-producing Niger Delta, and kidnapped 15 youngsters, police said on Tuesday.
The incident occurred early on Monday while the nursery and primary students were being driven to the Abayi International School in the southern state&${esc.hash}39;s commercial capital, Umuahia, state police spokesman Geoffrey Ogbonna told Reuters.
"The 15 students were being conveyed to school by the driver and the teacher that normally accompanies them when they were abducted," Ogbonna said.
"The kidnappers are demanding a ransom from the proprietress of the school. This is the first time schoolchildren have been kidnapped in Abia state. It is quite unfortunate."
Local media reported a ransom demand of 20 million naira (${esc.dollar}150,000), and the children&${esc.hash}39;s whereabouts are unknown.
Kidnapping of foreign oil workers and Nigerian civilians is relatively common in the delta, which has been riven for years by militias demanding a bigger share from central government of the oil wealth that flows from beneath its soil.
An amnesty that came into effect in the delta last year has reduced the overall levels of violence that curbed the output of Africa&${esc.hash}39;s largest crude oil producer.
However, three French oil workers were abducted in a raid an offshore drilling ship last week, and the seizure of a large number of children is a worrying departure by the criminal gangs that also roam the region.
Police in nearby Rivers State said on Monday a group of five women had been abducted two weeks ago by a criminal gang also believed to have come from Abia. The five are still believed to be in captivity.
Africa&${esc.hash}39;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. (Reporting by Ed Cropley, Tume Ahemba and Austin Ekeinde; Editing by Giles Elgood)
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