SYDNEY (Reuters) - The Australian competition regulator said on Tuesday it would not block the $3.1 billion acquisition by Google Inc of DoubleClick Inc, a U.S. Web advertising supplier.

The Australian Consumer and Competition Commission said its inquiry found the two companies were not close competitors in the provision of ad serving.

It added that other competitors in the market would put some constraints on the merged company.

The DoubleClick deal has also come under regulatory scrutiny in the U.S. and in Europe.

European regulators have extended their inquiry to allow remedies to possible competition problems to be tested, while experts in the U.S. have predicted it will win approval there.

The deal faces opposition from competitors Microsoft Corp and Yahoo Inc.

The Australian competition watchdog has taken Google to court in a separate case, alleging that sponsored advertising links on Google's Web site in 2005 amounted to misleading and deceptive conduct. The next hearing in that case is due on November 16.