Gunmen attacked an oil rig off Nigeria's coast on Monday, taking two Americans, two French and one Canadian hostage while wounding two other people, company and security sources said. The pre-dawn attack occurred in the country's turbulent Niger Delta region, the heart of one of the world's largest oil industries, and it was not immediately clear whether a ransom had been demanded.

"A security breach has occurred on the High Island VII jackup rig, which had recently arrived on location, preparing to commence infill drilling at the Okoro field," said a statement from Afren, the company that oversees the rig. "Two crew members are stable after receiving wounds to the leg, and have been evacuated by helicopter to a shore-based clinic. It is believed that five crew members have been taken hostage."

It did not provide the nationalities of the victims, but a company source said later that they included two Americans, two French and one Canadian. A security source also provided the same nationalities. Afren added in its statement that a second "security breach" occurred at a support vessel, but did not provide details. The statement said "the vessel and rig are both under the control of the company."

Preparations for drilling operations on the rig had been temporarily suspended.The security source said a crew member was shot in the leg after resisting the attackers. The Okoro field is located some 12 kilometres (eight miles) off the coast off Nigeria's Akwa Ibom State. Afren is headquartered in Britain and works with a local partner, AMNI International, while the rig is owned by Transocean.