US regulators are scrutinising Google's purchase of internet advertising giant DoubleClick following claims the deal threatens the privacy of internet users.

The Federal Trade Commission (FTC) has opened a preliminary antitrust investigation into the $3.1bn (£1.56bn) takeover, announced in April, amid fears the company would have too much control over the internet advertising market.

The inquiry was expected in many quarters, but Google's senior corporate counsel Don Harrison says the acquisition poses no risk to competition and should be approved.

'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 this industry will bring more relevant ads to consumers and more choices for advertisers and web site publishers,' he said.

DoubleClick tracking technologies have been criticised in the past for allowing the company to record which web sites surfers visit and which ads they click on in 'cookies'.

The Electronic Privacy Information Centre (Epic), a US pressure group, filed a complaint about the deal with the FTC late last month. It is concerned that Google could match DoubleClick's data with the search query histories it already records, creating highly accurate profiles of users.

'These profiles expose consumers to the risk of disclosure of their data to third parties, as well as public disclosure as evidence in litigation or through data breaches. We urge the FTC to halt the merger until it has fully investigated Google's planned use of DoubleClick's data after the merger,' said a spokesman for Epic.