`Russian hostage` in Nigeria not Russian: Embassy
Earlier a militant group demanding autonomy for the Niger Delta region claimed responsibility for the kidnapping, but didn't make any ransom demands.
Over 300 rebels attacked an offshore oil field belonging to Royal Dutch Shell.
The overseas workers as well as four Nigerians were seized after a three-hour gunfight.
It's the biggest attack on the oil industry since the new president came to power in Nigeria in April 2007.