Officials from Nigeria's southeastern state of Bayelsa say they are negotiating the release of two German and four Nigerian oil workers kidnapped by militants.

The six employees were abducted on Wednesday while traveling by boat to an offshore oil field. They work for the German firm Bilfinger Berger, a subsidiary of Royal-Dutch Shell.

The kidnappers - ethnic Ijaw militants - are demanding $20 million in ransom from Shell along with a promise to honor a previous agreement to give jobs and other benefits to local residents.

Communities in Nigeria's oil rich southern region have long complained they have been cut out of the money made from the resources extracted from their land. Militant groups frequently attack oil operations of multi-national companies to demand social services and better job opportunities.