Nigerian troops and militants have clashed in the oil-rich south following a recent spate of kidnappings in the restive region.
Militants from the Movement for the Emancipation of the Niger Delta say they killed nine soldiers during a 90-minute gunbattle Wednesday. The deaths could not immediately be confirmed.
The militants say they are sending another 500 fighters into Rivers State to begin what the group says will be a series of strategic attacks on the oil industry.
Tuesday, gunmen raided an oil company site, in Eket and kidnapped seven foreign oil workers. The kidnap victims are believed to include nationals of Britain, Romania and Indonesia.
And on Monday, 25 oil workers from Royal Dutch Shell were seized in a raid in Rivers State. The company said all of those hostages were later released.
Both the United States and Britain warned their citizens Wednesday about traveling to the Niger Delta.
Both countries say they believe that militants may be planning more attacks in the region.
Militant attacks have cut Nigeria's oil production by nearly a third this year.
The militants are demanding that Niger Delta communities get a greater share of the region's oil revenue. However, many of the recent kidnappings are believed to have been carried out strictly for ransom.
Some information for this report was provided by AFP and AP.