The Swiss company confirmed it made an “informal enquiry by telephone call” to Rio in July to gauge any interest in a merger.

“Rio Tinto responded that it was not interested in pursuing these discussions,” Glencore said.

“Glencore confirms that it is no longer actively considering any possible merger transaction with, or offer for the shares of, Rio Tinto.”

Under UK law, Glencore is not allowed to make an offer to Rio for six months, ruling out a takeover or merger offer until April 2015.

“Glencore, however, reserves its rights to make an offer in the future with the consent of the Takeover Panel, either with the recommendation of the board of Rio Tinto, in the event of a third party offer for Rio Tinto, or in the event of a material change in circumstances,” Glencore said.

Rio said its board unanimously decided that a merger was not in the company’s best interests, following consultation with financial and legal advisors.

The company informed Glencore of its rejection in early August and said there had been no further contact between the two parties.

However, the Bloomberg report that forced the companies to confirm the speculation suggested that while Glencore might not be “actively” pursing a deal with Rio currently, it could be laying the groundwork for a 2015 bid.

The report, citing people familiar with the situation, said Glencore approached Rio’s major shareholder Aluminium Corporation of China to gauge its interest in a potential combination but that approach came after Rio rejected a merger proposal in early August.

Glencore has a current market capitalisation of about £43.7 billion ($A79.9 billion), while Rio has a current market cap of £56.8 billion, making it an ambitious target for the Baar-based company.

But analysts agree that Rio would expect a substantial premium, something Glencore boss Ivan Glasenberg may not be prepared to offer.

“At the very minimum, Glencore would need to meet fair value,” IG Markets analyst Evan Lucas wrote yesterday.

“According to Bloomberg, this is between $A67 and $72.”

A valuation of $72 would imply a premium of almost 20%.

Lucas noted Glencore didn’t have the capacity to go hostile on a Rio bid.

“Its balance sheet would be heavily stretched to meet Rio’s current size, let alone if it went to fair value or beyond,” he said.

“In conclusion, therefore, the zero-sum offer looks shaky at best and a fair-value offer or more looks impossible.

“Ask yourself this – what does Glencore bring to the table that would entice Rio to accept? The simple answer is: ‘not much’.”

Analysts from SP Angel in London believe a Glencore offer would be a good deal for Rio.

“Glencore is a great fit for Rio Tinto,” SP said in a morning note.

“Regulators would have little to worry about and we reckon a deal could go through quite easily.”

SP believes Glencore could extract significant additional value from Rio’s portfolio, particularly the struggling divisions.

“Rio Tinto management are rightly focused on growing the iron ore business with many other parts of the business seemingly lacking in attention and investment,” it said.

“We see Glencore’s proactive management style as empowering local managers and helping to grow parts of the business which are lacking attention.

“Shareholders should be allowed a say in what happens to Rio Tinto and might well feel that better value could be determined under Glencore leadership.”

Rio is clearly gearing up for another Glencore approach, with the Australian Financial Review reporting that the company had engaged Macquarie Group for its defence.