The gunmen are demanding a ransom for the crew
Gunmen in Nigeria's oil-rich Niger Delta have hijacked a ship belonging to an US company and kidnapped its crew.
The militants are demanding a ransom of 30m naira ($259,000) for the boat and the crew, a military spokesman said.
The vessel, which ferries supplies for the oil company Chevron, was hijacked on Tuesday night near Port Harcourt.
Nine Nigerians, a Portuguese and a Ukrainian were sailing the vessel when the gunmen boarded it, according to military spokesman Lt Sagir Musa.
Nobody has so far claimed responsibility for the attack.
Nigeria is Africa's biggest oil producing nation, but frequent pipeline bombings and other attacks by militants demanding a bigger share of the profits have reduced output by 25%.
The remote and inaccessible creeks of the Delta are also home to criminal gangs who seize oil workers and attack pipelines for money.
Piracy in Nigeria's waters has also increased in the last two years, making its the most dangerous shipping area in the world.