"It is an industrial matter," Rear Admiral Anthonio Bob-Manuel told AFP. "If the situation gets to the stage when the civil police can no longer cope, then, and only then, would we be called for assistance."

A spokesman for the State Security Service, Nigeria's domestic intelligence body, also said no operation had taken place and that the navy was simply standing by as talks between management and unions continued.

Earlier Elijah Okougbo, deputy general secretary of the National Union of Petroleum and Gas workers (NUPENG), told AFP that he had heard that the workers had been pulled off at around noon (1100 GMT) on Wednesday.

But he refused to name his source for this information, and both the secretary general and the president of his union said that they were unaware of any naval operation.

The spokesman for rig owners Transocean Inc, Gary Cantwell, told AFP that no intervention had taken place by 1:00 pm (1200 GMT) Thursday.

Between 70 and 80 US and European oil workers have been trapped since April 19 on four offshore platforms by a blockade mounted by around 300 Nigerian strikers, who have refused a demand to quit the facilities.

Manuel, who is the navy's top commander in the area of sea where the US-owned rigs are moored, said that the navy was patrolling the area but that it had not taken to action to intervene.

"Our ships have always been there," he said.

Earlier NUPENG president Peter Akpatason had told AFP that his union would call a nationwide oil workers' strike if the navy moved in to break up the blockade.

SPACE.WIRE