US competition regulator the Federal Trade Commission has approved Google's $3.1bn (£1.5bn) takeover of DoubleClick.

The FTC, which cleared the acquisition by four votes to one, said the acquisition was "unlikely to substantially lessen competition" in the online advertising market.

Today's decision, which brings to an end an eight-month investigation into the proposed takeover, is a major victory for Google after rivals, notably Microsoft, campaigned strenuously that the deal would reduce competition.

"Because the evidence did not support the theories of potential competitive harm, there was no basis on which to seek to impose conditions on this merger," said the FTC in a statement.

"We want to be clear, however, that we will closely watch these markets and, should Google engage in unlawful tying [exclusively bundling the two companies services] or other anticompetitive conduct, the commission intends to act quickly."

However, the deal, which brings together Google's search advertising power with DoubleClick's online display ad operation, still faces an investigation by the European commission, which has set a deadline of April 2 to complete its review.

"The FTC's strong support sends a clear message: this acquisition poses no risk to competition and will benefit consumers," said the Google chief executive, Eric Schmidt.

"We hope that the European commission will soon reach the same conclusion, and we are confident that this deal will deliver more relevant ads for consumers, more choices for advertisers and more opportunities for website publishers."

Google's acquisition was approved earlier this year by the Australian competition and consumer commission and recommended for approval by one of three Brazilian regulatory agencies.

The company has said it cannot formally close the takeover until the European Commission clears the deal.

"There are benefits for advertisers but the industry as a whole in Europe will be concerned about the deal going forward because of dominance of Google," said Wayne Arnold, the European chief executive of digital ad agency Profero and chairman of the Institute of Practitioners in Advertising's digital group.

"And from a consumer perspective the vast amount of data that will be controlled in one players hands is a concern. However, the reality is that this deal will probably go through in Europe too now, despite lobbying".

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