Union leader Akpatson warned the navy not to get involved

Striking oil workers in Nigeria have started to release the first batch of nearly 300 staff being held on several offshore oil rigs, as a drawn-out labour dispute appears to be drawing to a close.

Helicopters returning the first of the workers who had been trapped on four rigs have arrived in Port Harcourt.

One British engineer, Paul Baker, expressed relief as he disembarked from the helicopter along with several Nigerian colleagues.

"There were no physical assaults, but there was psychological torture," he said.

Ninety-seven foreign workers, including 20 Americans and 30 Britons, along with 170 Nigerian workers have been trapped on the platforms since 19 April, caught up in a row over better working conditions and the dismissal of several workers.

Some crew members started running around the rig with a fire axe E-mail from oil worker One worker's e-mail diary

The BBC's Dan Isaacs, in Lagos, says it appears that Transocean, the American owners of the rigs, made few if any concessions to the strikers.

The issue had become an embarrassment for the government as concern increased for the safety of those being held, says our correspondent.

High tension

Although the union's demands have not been met, it has won a commitment from Transocean to hold further talks to discuss grievances.

Such disputes are not uncommon in Nigeria

The breakthrough in the dispute came after Nigeria's President Olesegun Obasanjo intervened, calling on the employers and the oil union to reach agreement urgently.

A spokesman for Transocean told BBC News Online he was "optimistic about the safe and prompt departure" of all the staff still on board the rigs.

Nigerian navy ships had been on standby in case they were needed to intervene - a move which increased the tension around the dispute.

In recent days there have been reports that the navy was planning to retake the platforms and remove the protesters.

These reports led to threats from Nigerian oil-workers' union leaders to hold a nationwide strike.

Such disputes are not uncommon in Nigeria, but they usually end peacefully after a protracted period of negotiation.

It is rare for hostages to be harmed.

Nigeria is the world's sixth largest oil exporter, with an Opec export quota of more than two million barrels per day.