Several foreign oil workers - believed to include three Britons - have been kidnapped in Nigeria.
Police in the Rivers state town of Ekit, outside the main oil city of Port Harcourt, said between four and seven foreigners were seized in the raid there, but they gave no details.
The BBC reported that three Britons, one Indonesian and one Romanian were abducted near the Exxon Mobil oil company's offices.
A top Nigerian security official confirmed the kidnapping but had no details.
Attacks by militant groups over the past year have caused a drop of nearly a quarter of Nigeria's usual output. Nigeria is Africa's largest petroleum producer.
Most people in the southern oil region remain deeply impoverished, fuelling the armed dissident groups.
More than two dozen oil workers have been kidnapped this year. Hostage takings generally end peacefully, with the targets returned unharmed.
Meanwhile, militants who attacked a military convoy escorting oil workers in the south freed nine of 25 Nigerians they had taken captive in the deadly raid. At least five people died in that attack.
Eurwen Thomas, a Royal Dutch Shell PLC spokeswoman, had no further details on the remaining 16 Shell subcontractors taken hostage.
In a separate incident, militants attacked a boat carrying oil-services workers in the same area of the swampy Niger Delta, wounding several soldiers, including one seriously, a private security official said.
