Rio Tinto will be forced to endure an independent review of its failure to meet cost and schedule guidance on Mongolia's Oyu Tolgoi copper mine expansion, after the mining giant's less powerful partners united in an extraordinary show of defiance.

The government of Mongolia and representatives of Canadian company Turquoise Hill Resources worked together on Monday evening to ensure an independent review would be conducted into the blowouts, which will see Rio's most important growth project delivered almost two years late and close to $US1.5 billion ($2 billion) over budget.