Mumbai: US anti-trust regulators have given conditional nod to mining giant BHP Billiton's $170 billion bid for Rio Tinto, the second-largest iron mining company, ahead of an expected ruling of an extended review by European regulators.

BHP Billiton is offering 3.4 of its shares for every Rio Tinto share, valuing Rio Tinto at around $170 billion.

BHP Billiton, the world's largest mining company, said the US Department of Justice and the US Federal Trade Commission had ended antitrust waiting period on the proposed deal early.

Under the Hart-Scott-Rodino Act, companies have to undergo a waiting period in order to determine if a takeover violates antitrust laws.

The justice department also concluded a review of the proposal without further action, the company said.

"We are very pleased that we have received notice of early termination of the Hart-Scott-Rodino Act waiting period and completion of the Department of Justice merger review," BHP Billiton's chief commercial officer Alberto Calderon said in a statement.

Regulators, however, have reserved their right to act against the merger deal in case of any fresh concerns over the deal during the offer period.

While regulators in the US, Australia, Canada, South Africa and other countries are studying the deal, the EC ruling would be of greater import.

The EC is expected to announce an extension of the investigation into a second phase, which could take another six months or even longer.

A merger of BHP Billiton and Rio Tinto would create the world's largest supplier of iron ore, coal and other resources that are currently in high demand.

Rio Tinto is vigorously resisting the offer.
Steel makers, especially in countries like China, Japan and Korea, have also expressed concerns that a combined BHP Billiton-Rio Tinto company would have too much control over raw material prices.

 Melbourne-based BHP Billiton, meanwhile, won a price increase of as much as 97 per cent from Baosteel Group, matching an agreement reached by the Rio Tinto Group.

Baosteel, China's top steel maker, will pay the revised prices with effect from 1 April, BHP said in a statement.

Iron ore prices have gained almost four-fold since 2001 to a record because of surging demand, mainly from China.

China buys about 50 per cent of BHP's iron ore and about 55 per cent of Rio's. The country is expected to increase imports by 14 per cent to 435 million tonnes this year.