Mobil Producing Nigeria, a subsidiary of US oil group ExxonMobil, said Thursday one person was killed during an attack on one of its convoys in the southern Nigerian state of Akwa Ibom
Unknown gunmen attacked the convoy on the road between the town of Eket and the Qua Iboe oil export terminal Wednesday, the company said in a statement.
"The victim is not an MPN employee and his identity cannot be ascertained at this time," the company added.
State government and the security agencies had launced investigations into the incident, it added.
Mobil Producing Nigeria is the biggest foreign operator in the country, producing around 780,000 barrels a day.
The past three years have seen an upsurge in violent attacks on oil firms and kidnapping of local and foreign workers in Nigeria's oil-rich Niger Delta.
The unrest has reduced Nigeria's oil output by more than one quarter.
Production this year has averaged just over 2 million barrels a day, due to the situation in the Niger Delta, Nigerian president Umaru Yar'Adua said earlier this week.
That compares with 2.6 million barrels two years ago.