Nigerians with assault rifles overran a navy base early Tuesday, taking several troops hostage, and occupied a nearby oil facility belonging to a subsidiary of Royal Dutch Shell PLC, a police official said.

Hafiz Ringim, police commissioner for Nigeria's southern Bayelsa state, did not how many troops were taken hostage or how many attackers were involved.

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"The government is attempting to negotiate with (the attackers). We have officers on their way down there now," Ringim said. "There is quite a number of them. There have been no injuries yet."

Shell officials did not immediately comment.

A series of attacks and kidnappings in Africa's largest oil producer have cut Nigeria's production by more than a quarter so far this year.

Despite the Niger delta's massive energy resources, most people in the region are mired in extreme poverty. Some have resorted to kidnappings and attacks that grab international attention in order to get a share of the wealth.

More than two dozen foreign oil workers have been kidnapped this year. Hostage takings generally end peacefully, with the targets returned unharmed.

Groups have also sabotaged pipelines and oil installations in the West African country, the fifth-largest supplier of crude to the United States.