Google faces a competition inquiry into its planned $3.1 billion (£1.6 billion) purchase of DoubleClick, after the US Federal Trade Commission (FTC) confirmed it would launch a review.

The Californian search group won control of DoubleClick, which places advertisements online and helps customers monitor their impact, after a fierce bidding battle against rival Microsoft.

Wall Street analysts were widely anticipating that the FTC would step in to review the deal.

The acquisition of DoubleClick would boost Google's presence in the online advertising market, which it already dominates. Microsoft had raised objection's to Google's acquisition as has Sir Martin Sorrell, chief executive of the world's biggest advertising agency WPP. Sir Martin said Google may face conflicting interests if it acts as both a seller and buyer of online advertising space.

Don Harrison, Google's senior corporate counsel, said: "Numerous independent analysts and academics have determined after looking at this acquisition that the online advertising industry is a dynamic and evolving space... and that rich competition in the industry will bring more relevant ads to consumers and more choices for advertisers and website publishers."

He said he expects the acquisition to be approved.

Electronic Privacy Information Center, a Washington-based privacy group, has previously called on the FTC to investigate the privacy implications of the deal.

Eric Schmidt, Google's chairman and chief executive, predicted earlier this month that the deal would clear all regulatory hurdles.

Google announced the agreement to buy DoubleClick last month. Rival groups have since agreed a string of deals to buy online advertising specialists. Yahoo is paying $680 million to buy Right Media, WPP has signed a $649 million agreement to buy 24/7 Real Media and Microsoft is buying aQuantive for $6 billion.

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