PORT HARCOURT, Nigeria, Oct 21 (Reuters) - Gunmen have kidnapped two children of a Nigerian oil worker in the Niger Delta oil city of Port Harcourt, police said on Tuesday.

The children were being driven to school when they were abducted in the Abuloma area of the city and taken to an unknown location, said Rita Abbey, police spokeswoman for Rivers state, of which Port Harcourt is the capital.

"They were kidnapped this morning by gunmen who were in a black jeep. They are a boy and a girl aged between 7 and 9, children of a Nigerian Shell worker," Abbey said.

Kidnappings are common in the Niger Delta, particularly since armed groups seeking greater control of the region's natural wealth launched a campaign of sabotage against the oil industry in early 2006.

The delta, a vast network of shallow creeks flowing into the Gulf of Guinea, is the hub of Africa's biggest oil and gas industry, which produces around 2 million barrels of crude per day. The unrest has slashed output by around a fifth.

Criminal gangs have taken advantage of the breakdown in law and order, funding themselves through a lucrative trade in stolen oil and frequently kidnapping expatriates, local businessmen and politicians or their relatives, for ransom.

Police said no group had yet claimed responsibility for the latest kidnappings.

About a dozen children of local oil workers and politicians, including toddlers, have been kidnapped around Port Harcourt in the last two years. They were freed unharmed after money changed hands, private security sources and rights groups said. (For full Reuters Africa coverage and to have your say on the top issues, visit: http://africa.reuters.com/ ) (Reporting by Austin Ekeinde; Writing by Tume Ahemba; Editing by Nick Tattersall)

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