Gunmen attacked a Russian oil tanker off the coast of Nigeria's volatile Niger Delta but the crew managed to steer the vessel to safety, security sources said on Tuesday.

Gunmen in speedboats attacked MV Katanga, chartered by a Murmansk-based company, about 20 nautical miles off Nigeria's southern state of Rivers on Monday in the latest act of piracy in the region.

"Gunmen in at least three speedboats attacked Russian oil tanker MV Katanga in Bonny Fairway Buoy. It managed to outmanoeuvre the attackers and escape to safety," one security source said.

Nobody on board was wounded and all crew members were accounted for, he said.

Russian news agency Ria Novosti quoted a company source as saying the attackers, who were armed with automatic weapons, beat a retreat after the tanker sounded its alarm and switched on its floodlights.

Nigeria has one of the world's highest levels of piracy, particularly off the Niger Delta, the heartland of Africa's biggest oil and gas industry where criminal gangs regularly blow up oil facilities and kidnap expatriate workers.

Two Russian expatriates were rescued last week by Nigerian soldiers after escaping from a militant hideout where they had been held for two months.