PotashCorp said it was in talks with several other suitors over a tie-up, heightening speculation that BHP Billiton will face a higher offer, or spoiler deal, to its hostile $39bn offer for the Canadian group.

PotashCorp said it had received interest from "a number of third parties", attracted both through uninitiated approaches and the group's own efforts to give shareholders an alternative to BHP's bid, pitched at $130 a share.

"The PotashCorp board, together with PotashCorp's management team and financial and legal advisors, have been working to evaluate a range of strategic alternatives that may enhance shareholder value," the company said.

The company, the world's top potash producer, said it was pursuing talks with "several" of the rival suitors, adding that "superior offers, or other alternatives, are expected to emerge".

PotashCorp shares rose 0.3% in New York to close at $150.20, their best finish for nearly two years, indicating increasing hopes from investors that BHP's initial offer would fail.

Alternative options 

The statement followed reports that that Canadian group had been contacted both by Sinochem, the Chinese state-owned chemicals giant, and Vale, the South American mining group which acquired a portfolio of phosphate assets in its native Brazil through a series of deals earlier this year.

While topping BHP's $130-a-share bid is seen as a stretch for either of these companies, analysts have noted that PotashCorp may be able to avoid a full takeover by taking on a minority shareholder in a blocking manoeuvre.

Two years ago, Rio Tinto fought off a BHP bid after attracting China's Chinalco, which is also state owned, as a minority investor.

Rio itself also has been named as a potential rival suitor for PotashCorp, after being reported two weeks ago as being interested in a stake in Russian potash group Uralkali.

'Wholly inadequate'

PotashCorp's revelation came as it restated its opposition to BHP's bid, dismissing it as "wholly inadequate", and as an "ill-disguised attempt to exploit an anomaly" in stock market valuations.

"BHP intentionally launched the� offer just as the fertilizer industry is emerging from an unprecedented demand decline associated with the global economic downturn, in order to seize the value that PotashCorp is poised to create," the statement said.

The deal offered a "wholly inadequate" takeover premium of 16%, compared with PotashCorp's share price before the bid was announced.

Furthermore, BHP's offer did not meet the criteria of a "permitted" offer, as laid down in rules released two weeks ago and aimed at clipping the wings of hostile bidders.