Rio Tinto challenged BHP Billiton today to make a formal bid to create a mega-mining house or walk away.
Rio said it asked Britain's Takeover Panel to set a deadline under a "put up or shut up" rule by which BHP would have to formalise its approach, more than a month after BHP's $140 billion (£68.4 billion) three-for-one share proposal was made public.
A combined BHP-Rio would hold about 27 per cent of the world market for iron ore. It would also control the global flow of coal, copper, uranium and diamonds.
Rio has rejected BHP's overture, which it received in the form of letter, as "out of the ballpark", and it has declined to meet BHP face-to-face to discuss a merger.
In China, trading in the country's biggest steelmaker, Baoshan Iron and Steel was suspended today amid speculation that Chinese companies could become involved in a bid for Rio.
Baoshan has denied preparing a counterbid.
Investment group Blackstone has denied a British newspaper report it was planning a counterbid for Rio with a consortium believed to include China's sovereign wealth fund.