If a country's antitrust regulators reject a merger and acquisition plan but it still goes ahead, the deal would be in conflict with that country's laws, China's antitrust chief said Tuesday in response to concerns about the proposed joint venture between Rio Tinto PLC (RTP) and BHP Billiton Ltd. (BHP).

Shang Ming, chief of the Anti-monopoly Bureau at the Ministry of Commerce, said in a rare public speaking engagement at a local university that the bureau hasn't yet taken a position on the planned iron ore joint venture between the companies, after Rio rejected a Chinese bid for massive investment.

His comments come after the Ministry of Commerce said Friday the Anglo-Australian miners would be expected to undergo the Chinese government's antitrust review if the nature of the two companies' joint venture requires it.

BHP and Rio Tinto entered into the joint venture for their iron ore supply operations last week after Rio Tinto terminated its planned US$19.5 billion alliance with Aluminum Corp. of China, or Chinalco.

"So far, we don't have related experience on this kind of case," Shang said. "Just because there is a merger, it doesn't mean we will get involved."

He said an anti-monopoly review comes into play if a merger and acquisition plan shows "industry concentration," and regulators can either allow the merger to take place with conditions or reject it.

"So if you disallow it, and it goes ahead, then you are in contravention of a country's law," Shang said.

His comments echo those of other commerce ministry officials in recent days, but it is the first time the bureau directly involved in reviewing M&A cases in China has commented on the deal between the Anglo-Australian miners.

Shang, who took up his current post last year after being chief of the ministry's Department of Treaty and Law since 2003, said there will be more regulations to support China's nearly one-year-old anti-monopoly law in the near future.

These will include defining when a merger deal becomes significant enough to trigger an antitrust review, he said. The rules will govern when companies need to notify the Chinese government of the possible antitrust implications of a deal and also how to determine which markets would be affected, he added.

Shang, a career bureaucrat in the government's foreign trade sector since the early 1980s, also said the bureau hasn't received an application from China Eastern Airlines Corp. (CEA) and Shanghai Airlines Co. (600591.SH) about their proposed merger.

Over the weekend, China Eastern Chairman Liu Shaoyong said the two airlines have set up a joint taskforce to work on the proposed merger and will present a formal report to shareholders within 20 days.

China's anti-monopoly law took effect at the start of August and the country's regulators, which include the Ministry of Commerce, the State-owned Assets Supervision and Administration Commission, and the National Development and Reform Commission, have issued draft rules seeking public comment.

Many of the draft rules have yet to formally go into effect.

-Juan Chen and Chuin-Wei Yap contributed to this story, Dow Jones Newswires; 8610 6588-5848; juan.chen@dowjones.com