Gunmen attacked a boat carrying oil workers to an offshore rig in waters off Nigeria's unruly southern oil region, wounding six passengers, officials said Friday.
Security forces drove off the attackers, said a private security official, speaking on condition of anonymity because of company prohibitions on dealing with the media.
Another security official, also speaking on condition of anonymity for the same reason, said three Nigerian workers initially feared kidnapped in the overnight raid had been found hiding under the vessel's engine housing.
A military spokesman, Maj. Sagir Musa, confirmed an attack, but had no details.
More than 150 foreigners have been kidnapped over the past year in the southern region where crude is pumped in Africa's largest producer. Stepped-up violence has trimmed Nigeria's daily production by about one quarter, helping send global crude prices higher.