BRUSSELS, Jan. 25 (Xinhua) -- The European Union (EU) Monday opened an antitrust investigation into the mining deal between Anglo-Australian mining companies BHP Billiton and Rio Tinto to decide whether the deal obstructs competition.

BHP Billiton and Rio Tinto, respectively the second and third largest producers of iron ore in the world, signed a deal on December 5, 2009 to establish a production joint venture covering the entirety of both companies' Western Australian iron ore assets.

The European Commission, the executive arm of the EU, said in a press release that it will "in particular examine whether the joint venture would have a negative effect on competition on the worldwide market for seaborne iron ore".

According to the Commission, there is no binding deadline to complete the investigation and the duration of the probe depends on a number of factors, including the complexity of the case, cooperation from the undertakings concerned and exercise of the rights of defence.

It is the second time that the Commission investigated the two companies. In 2008, the Commission examined under the EU Merger Regulation the full acquisition of Rio Tinto by BHP Billiton. The transaction was abandoned by BHP Billiton on November 26, 2008.