The US Federal Trade Commission (FTC) has approved Google's proposed acquisition of online advertising firm DoubleClick.

The approval leaves the European Commission as the last hurdle still facing the $3.1bn purchase of DoubleClick from a San Francisco private equity firm.

"The FTC's support sends a clear message that this acquisition poses no risk to competition and will benefit consumers," said Google chairman and chief executive Eric Schmidt. "We hope that the Commission will reach the same conclusion."

Google announced its intention to purchase DoubleClick in April, but the deal drew the attention of regulatory agencies worldwide.

Privacy groups, along with rival Microsoft, petitioned against the acquisition, arguing that it would give Google a huge database of customer information that would threaten user privacy.

The Commission declined to address the privacy concerns, saying that its interest in the deal was limited to antitrust matters.

The Commission did note, however, that the privacy concerns were not limited to Google and "extend to the entire online advertising marketplace".

Although the FTC did not rule on the privacy implications, Sterling Market Intelligence founder and principal analyst Greg Sterling expects the European Commission to pick up where the US left off.

"I would guess that the Europeans will force Google to take some concrete measures on privacy as a condition of approving the deal, if it is to be approved," Sterling wrote in an article posted to a company blog.

The Commission is due to make its decision on the deal by 2 April 2008.