Rio Tinto will spend an extra $US80 million ($117 million) fixing glitches within its flagship iron ore division as it warns Canberra that high energy prices have its Australian aluminium smelters “on thin ice”.

Surging iron ore prices propelled Rio to a $US4.93 billion underlying half year profit, the company’s best since 2014, and enabled Rio to return $US3.5 billion of cash to shareholders.