More than 70 European and American oilmen have been stuck for 12 days on four oil platforms off Nigeria's south coast, hostages to a dispute between Nigerian workers and the rigs' US owners.

On Thursday a senior naval officer in Port Harcourt, the nearest base to the hijacked rigs, told AFP that naval vessels 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.

The strike began on April 19 as a protest over the sacking of five union members for alleged theft, but the workers' unions say they are now willing to return to work if management drops a demand that they evacuate the rigs.

The navy has promised to try and resolve the crisis peacefully, but its threatened intervention has angered trade unionists, who issued a May Day warning of an industry-wide stoppage.

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.

"If they use the navy the situation would exacerbate. We would react and our reaction might not be too palatable. It could lead to the entire industry going on strike," he said.

An 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.

Akpatason said he was in talks Thursday with the state-run Nigerian National Petroleum Corporation (NNPC), which operates as a joint venture partner with foreign multinationals in most Nigerian fields.

"They're showing interest in resolving the matter," he said, expressing the hope that the state firm could help reopen talks with Transocean.

Wednesday's talks failed because the protesters would not agree that the four rigs be "down-manned", or completely evacuated.

The union says its members are ready to end their action, but only if they are replaced by more NUPENG staff. Transocean is demanding that they leave for dry land before any new crew is shipped out.

Akapatason said that his members were concerned that the workers would be laid off once they left the rigs, if no colleagues were left behind to launch a new protest in their support.

"Management are saying 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," he said.

Earlier in the crisis diplomatic sources told AFP that there were 97 foreign workers -- 35 Britons, 21 US citizens, six French and some others -- on board the four rigs. Some have now been released.

The union chief told AFP he estimated that between 70 and 80 expatriates were still trapped -- along with 400 Nigerians, three quarters of them protesters -- but denied they were being held hostage.

The Nigerian navy's spokesman, Captain Sinefi Hungiapuko, told AFP Wednesday that the navy was deploying to the seas around the rigs, but that they would seek to end the standoff peacefully.

Transocean spokesman Guy Cantwell denied this. "The navy has told us that they are not sending their ships to our rigs," he told AFP.

SPACE.WIRE