BHP Billiton and Rio Tinto remain committed to the proposed merger of their Pilbara iron-ore operations, in the midst of uncertainties created by government's proposed 40 per cent super-profits tax.

BHP Billiton chief executive Marius Kloppers said that he had recently met with Rio Tinto's chief executive Tom Albanese to discuss the proposed merger. Kloppers said Albanese assured him of Rio Tinto's intention to meet the December 31 deadline for the deal as it stands.

The two mining companies signed an agreement in December 2009 to create Australia's second biggest company behind BHP Billiton, with a value of about $US116 billion. Under the agreement, BHP Billiton will pay Rio Tinto $US5.8 billion as compensation for contributing more iron-ore.

There is no final agreement on the proposed 50-50 joint venture yet. Both BHP Billiton and Rio Tinto agreed that if there is no final agreement by the end of the year, either party has the right to walk away from the deal. If either side walks away before then, a $US275 million fee is incurred.

The planned merger, which has been fiercely opposed by Asian steel mills, awaits approval from local competition regulator, European Commission and Japanese and Korean regulators.

Kloppers said he still wanted to do the iron-ore production venture with Rio Tinto. "We have many hurdles to jump through and the tax brings in uncertainty."

Rio Tito spokesperson David Luff yesterday said Rio "remains committed to the deal."

Kloppers has openly criticised Canberra's proposed super-profits tax, saying the proposal is a ''retroactive tax grab'' and again raised concerns that it would ''limit investment in the long run and decrease prosperity."