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On Thursday, Rio Tinto rejected proposals to create a mining giant worth about $350bn (�168bn).

The proposals include a promise to have a $30bn (�14bn) share buyback if the deal goes ahead.

China Development Bank has denied reports that it has bought a stake in Rio Tinto.

As one of the mining industry's biggest customers, it had been suggested that the Chinese government wanted a say in the process.

Weekend newspapers also reported that BHP is considering mounting a hostile takeover bid.

A Rio Tinto spokesman reiterated that the approach from BHP was still "well out of the ballpark" and significantly undervalued it.

But BHP said it would now seek to gather support for its takeover plans.

"BHP Billiton now considers it appropriate to make BHP Billiton and Rio Tinto shareholders aware of its proposal so it can seek their support for discussions between the two companies," BHP said.