Police were investigating reports that gunmen seized two more foreign oil workers, two days after four Norwegian and Ukrainian workers were seized from a boat in the latest violence targeting the petroleum industry in Africa's largest crude exporter.
The two oil workers were reportedly seized in the oil-industry center of Port Harcourt, said Irejua Barasua, a police spokeswoman. No more details were immediately available.
Southern Nigeria, where most of the country's crude is pumped, has seen violence against the petroleum industry rising in recent days. The kidnappings and attacks have forced a nearly 20 percent reduction of Nigeria's usual 2.5 million barrel daily production, helping send crude prices soaring in international markets.
Late Tuesday, gunmen stormed a boat heading to oil rigs far from Nigeria's coast, kidnapping four Norwegian and Ukrainian workers during a raid on the supply vessel owned by a Norwegian shipping firm, Trico Supply, company spokesman Bjorn Endresen said in Norway.
Trico Marine Services, the company that owns Trico Supply, said it had made contact with the kidnapped Norweigians, and negotiations had begun for their release. "They are well," the company said in a statement.
There was no immediate word on the Ukrainians.
Andy Oputa, a security official for Nigeria's Bayelsa State, confirmed Tuesday's kidnappings and said government negotiators had been sent to the restive Niger Delta region, where most of the crude is pumped.
Another state official said the capture took place nearly 50km from shore, with gunmen boarding the ship as it headed to offshore oil rigs. There was no immediate claim of responsibility.
Endresen said there were 11 other crew members aboard the ship at the time of the kidnapping, but did not give further details.
"All I can tell you is that we're working hard, putting all of our efforts to solving this case," Endresen said.
Last week, militants wearing camouflage uniforms took a German oil industry worker hostage, spiriting him away on a boat into Nigeria's troubled delta region.
A group calling itself the Movement for the Niger Delta People claimed responsibility for that kidnapping, but police said the group was unknown.
Militants have kidnapped oil workers to bargain for a greater share of the wealth from Africa's largest crude producer.