Naval officers deployed near the crisis zone told AFP they were ready to launch an operation to secure the oil rigs, but their commander said that no action had yet been taken to ensure the oilmen's safe release.

Meanwhile, the platforms' US owner Transocean Inc told AFP that it had asked Nigeria's President Olusegun Obasanjo to intervene to break the deadlock in talks between the firm and Nigerian union leaders.

Between 70 and 80 European and American oilmen have been stuck on four oil platforms off Nigeria's south coast since April 19 when their striking Nigerian colleagues blocked helicopter pads and access to supply ships.

None of those on board are thought to have been hurt, but trapped British workers have said in e-mails to their union that the situation is tense and that strikers have threatened to set fire to the platforms.

On Thursday a senior naval officer in Port Harcourt, the nearest base to the hijacked rigs, told AFP that naval forces were ready to move in and that he expected the crisis to be over "today or tomorrow".

"We are still discussing things. We are awaiting a decision," he said. Officers said they hoped to be able to end the standoff without violence.

The navy's commander in the area, Rear Admiral Anthonio Bob-Manuel, said that no operation had yet been launched.

"It is an industrial matter," he told AFP in Lagos. "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."

Talks between rig owners, Transocean Inc, and Nigeria's National Union of Petroleum and Natural Gas workers (NUPENG) broke down Wednesday.

"We have advised that they do not use the navy," NUPENG president Peter Akpatason told AFP on Thursday. "The situation would exacerbate. It could lead to the entire industry going on strike."

A strike in the world's sixth largest oil exporter would send tremors through international oil markets and cripple Nigeria's economy, which relies on exports of crude oil for 96 percent of foreign revenue.

The current action began on April 19 as a protest over the sacking of five union branch officials for "alleged financial irregularities".

Although some expatriate staff have been allowed to leave during the dispute, diplomats believe that 35 Britons, 21 Americans, six French and several more foreigners are still barricaded in by the strikers.

NUPENG denies that the men are hostages, but says its members fear they will be sacked if they allow the rigs to be evacuated without waiting for a fresh unionised crew to arrive, as Transocean has demanded.

"Management say everybody should leave the rig and thereafter they will decide when to come back and who will come back. We fear the decision to downman is born of a desire to lay off workers," Akpatason said.

Transocean Inc spokesman Gary Cantwell would not rule out this possibility. "I can't speculate on anything that might happen to them. They have got themselves into a situation of illegality," he told AFP.

Cantwell said that a Transocean official had contacted Obasanjo and asked him to intervene in the dispute by talking with Nigeria's umbrella trade union body, the Nigeria Labour Congress (NLC).

Obasanjo met with NLC officials at Nigeria's main May Day parade in Abuja, but it was not known whether he had discussed the strike.

And NLC general secretary John Odah said that the union had already called on the rig workers to suspend their action.

"We will continue our discussions with the strikers through NUPENG." he told AFP. "Hostage taking is not in the best interest of anybody. It does not help and the NLC does not support it."

SPACE.WIRE