Talks aimed at averting a strike by workers at the giant Grangemouth oil refinery have broken down.

A two-day strike by up to 1,200 workers at the site in Scotland will now go ahead on Sunday and Monday, threatening fuel supplies.

Officials from Unite met for the past two days with bosses from Ineos, which owns Grangemouth, at the conciliation service Acas.

But the union announced that the talks had failed to find a breakthrough in a dispute over pensions.

The strike has been called in protest at plans by Ineos to close its final salary pension scheme to new workers and to make other changes to its pensions.

A union spokesman said: "Unite's negotiators were disappointed with the company's refusal to withdraw controversial pensions plans and therefore the two-day strike will go ahead.

"Although the strike has not been averted, Unite and the company have reached an agreement that will maintain the safety of the site and the integrity of the plant for the duration of the dispute.

"Acas has advised both parties of their availability should assistance be required."

A statement from Acas said: "Acas has advised both the company and Unite that the opportunity to seek assistance of Acas to pursue an agreement has been offered."

Ineos has already started shutting down Grangemouth, the biggest refinery in Scotland, and warned of fuel shortages from later this week if the strike went ahead.