PORT HARCOURT, Nigeria - Armed militants kidnapped five Koreans and killed several soldiers in an attack on a small natural gas plant in Nigeria's southern delta on Wednesday, authorities said.
The Movement for the Emancipation of the Niger Delta (MEND) claimed responsibility and said the Koreans would be freed in exchange for a jailed militia leader who is on trial for treason and was denied bail by a Nigerian court on Tuesday.
The attack on the plant operated by Royal Dutch Shell comes three days after eight foreign oil workers were released by a different group of kidnappers, and is the latest sign of rising militancy in Africa's top oil producer.
MEND, whose attacks have already forced the closure of a quarter of Nigerian oil output since February, had previously demanded the release of militia leader Mujahid Dokubo-Asari as one of several conditions for ending the violence.
"The government of Nigeria may be interested more in a prisoner exchange rather than releasing the person whose release we have demanded," MEND said in an emailed statement.
Dozens of militants came in nine boats armed with assault rifles and rocket propelled grenades, engaging troops in a firefight lasting almost half an hour, a navy source said.
The tactics and firepower were similar to those used in a wave of militant attacks in January and February.
"In the next few weeks our attacks will increase (in) frequency with the destruction of several facilities of crucial importance to the oil industry," MEND said, advising workers to leave the oil-producing wetlands region in Nigeria's far south.
MEND, whose leadership is unknown, is pressing for more local power over the Niger Delta's oil resources and has said it aims to bring the Opec nation's exports to a complete halt.
Energy-hungry South Korea has growing interests in Nigeria, the world's eighth largest oil exporter, and earlier this year won exploration rights in return for billions of dollars of investment in Nigerian infrastructure.
In Wednesday's pre-dawn raid, MEND said it captured and burnt a houseboat used by army and police assigned to protect the Cawthorne Channel natural gas plant, and several security forces were killed in a fierce firefight.
The militants then kidnapped the five Koreans, whom they said had been taken to a MEND base where they were safe and would not be harmed unless the base was attacked.
As the militants left the facility, they came under attack from four Nigerian army boats. The militants said they sank one of the boats, killing at least five of its six occupants, while the other boats suffered an unknown number of casualties.
A security source said nine navy staff and a policeman were killed. Military spokesmen confirmed four dead.
MEND said one of its fighters was killed, but a navy source said they fished four enemy corpses from the water.
In Seoul, a Foreign Ministry official said three of the kidnapped South Koreans worked for Daewoo Engineering and Construction Co and the other two were with Korea Gas Corp.