Global miner Rio Tinto has confirmed that resources group Glencore has approached it about a merger but says it’s rejected the offer.

The approach was made in July.

Such a merger would create the world’s largest mining company.

Rio Tinto said, in a statement on Tuesday, that its board, after consultation with its financial and legal advisers, concluded unanimously that a combination was not in the best interests of its shareholders.

Rio released a statement after press reports overnight said Glencore had reached out to the former’s largest shareholder China’s Chinalco.

Rio said no discussions were taking place with Glencore.

“The board’s rejection was communicated to Glencore in early August and there has been no further contact between the companies on this matter,” it said.

Rio Tinto chairman Jan du Plessis said the board believed that the continued successful execution of Rio’s strategy would allow the company to increase free cash flow significantly in the near term and materially increase returns to shareholders.

A combined company would go past BHP Billiton and be worth an estimated $US160 billion ($A173.11 billion) with market leading positions in iron ore, copper, nickel, zinc and coal.

Rio is the world’s second-largest producer of iron ore while Glencore is not a significant producer of that commodity.

It has been suggested Glencore chief executive Ivan Glasenberg is frustrated with not being able to finalise a NSW coal joint venture with Rio that would achieve significant savings through synergies.