Maritime Sovfracht Bulletin said the Hercules tugboat is owned by Sweden's Marine Carrier AB and was working for Italian oil services company Saipem SpA, a subsidiary of oil and gas multinational Eni SpA.
The militants, who belong to the Movement for the Emancipation of the Niger Delta, which has been linked to several attacks on foreign oil workers, are demanding that Saipem pay a ransom for the crew's release, the site said.
The Russian Embassy in Nigeria's capital Lagos has tightened security for staffers following the incident, the embassy press secretary said.
"In view of this situation, embassy staff are forbidden from independently travelling to the coast," Igor Popov said.
Russian embassy advisor Viktor Goncharov told the radio station Vesti-FM that according to preliminary information, there may be only two Russians among the hostages. The embassy is working closely with Nigerian law enforcers, who have established contact with the hostage-takers, he said.
