Workers at a giant Indonesian gold and copper mine owned by US company Freeport-McMoRan said Friday they would not return to work, three weeks after officially ending the country's longest-ever strike.

The workers' union said that several of Freeport's subcontractors had not paid more than 900 employees at the mine, in the restive eastern province of Papua, during a three-month strike that ended in December.

"Under Indonesian law, workers should be paid during a legal strike. If any of the contractors are not paid for that three-month period, then we will stop sending our workers back to the mine," union spokesman Virgo Solossa told AFP.

More than 8,000 workers and 1,600 contractors of the mine's 23,000 workers went on strike in September, slashing production by 50 percent.

The company claimed force majeur – a legal declaration of extraordinary circumstances enabling it to avoid liability on existing orders – as it was unable to deliver shipments to some customers.

The workers agreed to return to the mine on December 17 after negotiating a 37 percent pay increase on wages that started at $1.50 an hour for unionised members and better conditions for contractors.

Freeport Indonesia spokesman Ramdani Sirait denied the delay in resuming work was due to a dispute, citing safety reasons for sending workers back slowly to the mine.

At least eight people were killed around the mine in ambush attacks and a clash with police during the strike. The company said it aims to have all workers back by January 16 and reach full capacity in the following weeks when all damaged pipelines are repaired.

The strike was one of a wave of industrial actions across Southeast Asia's largest economy, where the cost of living is rising and a burgeoning middle class is demanding a greater share of the nation's economic success.

The workers claimed to be Freeport's lowest-paid employees in the world, including those at mines in Africa and South America.