Pirates have seized an oil tanker off the coast of Nigeria's oil-rich southern delta and kidnapped the foreign crew.
The attack happened off the coast of Port Harcourt, security sources said.
An unknown number of foreign crew members remained held as the pirates offloaded the tanker's oil cargo.
The tanker was identified as the MT Halifax, a ship flagged out of Malta.
Analysts say the area has seen a growing trend of oil tanker hijackings as pirates target legal and illegal oil shipments moving out of Nigeria.