Rio Tinto has assets across the world.

It has urged the UK's Takeover Panel to invoke the so-called "put up or shut up" rule which imposes a time limit on would-be buyers.

Rio has already dismissed BHP's $130bn (�63.2bn) approach as too low.

Separately, reports say that Xstrata - the world's sixth largest miner - is open to talks with potential suitors.

The London-listed firm has hired advisers to listen to interested parties, the Financial Time said.

Booming demand from China and India has made commodities firms attractive, with analysts expecting more consolidation in the sector.

Rival bid?

Rio said that if the ruling was made, it would mean that BHP must "either announce a firm intention to make an offer... or announce that it does not intend to make an offer".

Most analysts believed that the move was designed to break the stalemate between the two companies - but that BHP would have to sweeten its offer if it were to have any success.

BHP declined to comment, saying it was a matter for the Takeover Panel.

In an attempt to defend itself against BHP, Anglo-Australian firm Rio has already said it will look to boost shareholder value by selling off $30bn-worth of its business, including two uranium projects in Australia and a zinc, lead and silver mine in the US.

Analysts say that Rio's refusal to team up with BHP is indicative of its conviction that mineral and metal prices will stay high for years to come, fuelled by strong demand from emerging economies such as China and India.

A report in the Daily Telegraph earlier this week said that US private equity giant Blackstone was planning a rival bid for Rio Tinto.

The paper said that Blackstone was creating a consortium, thought to include a Chinese sovereign wealth fund, to make the bid.