The kidnappers are dissatisfied with Shell's implementation of an agreement to provide nine communities bordering oil fields with jobs and basic social benefits, Simon Buerke, a spokesman for the Royal Dutch/Shell Group of Cos., said by telephone from London.

The Iduwuni National Union for Peace and Development group claimed responsibility for the Wednesday kidnapping of the six employees of a German contractor for Shell.

"We agreed ... to undertake some development projects, some have been completed, some have not," said Buerke.

The projects have not been executed as quickly as the company would want because of the "large capital outlay" required, he said.

Shell has put in place a micro-credit scheme to help provide jobs and improve marine transport among the communities, and was currently building schools and other educational projects, he added.

Shell says it has scheduled "an engagement session" for mid-July with the protesting communities, aimed at resolving differences.

Steve Azaiki, secretary of the Bayelsa state government in charge of the area where the hostages were taken told The Associated Press that authorities have sent officials to the protesting communities to secure the hostages' release.

Azaiki said the government will not tolerate such unlawful acts, but accused Shell of reneging on an agreement reached to secure the release of a Croatian worker last December.

"You can't have an understanding and not honor it. That means creating security problems for the government," Azaiki said.

Criminals frequently hit oil operations in the Niger delta with hostage takings and sabotage. Most captives are eventually released.

Nigeria exports some 2.5 million barrels of oil daily, making it Africa's leading oil producer, the world's seventh-leading exporter and the fifth-biggest source of U.S. oil imports.