BRUSSELS, May 10 (Reuters) - Regulatory authorities should look closely into Google's buy of mobile advertising leader AdMob as this reinforces Google's market power, the head of WPP , the world's largest advertising group by sales, said on Monday. Last November, world number 1 search engine Google unveiled the $750 million deal to buy AdMob, which controls about one third of the market for putting ads on mobile applications and web pages. Sources familiar with the U.S. antitrust inquiry into the acquisition have told Reuters they were concerned about the impact of the deal on applications developers. "It (regulatory investigation) should be rigorous. Our clients will welcome a close look," WPP chief executive Martin Sorrell told Reuters on the sidelines of the World Economic Forum on Europe. "I don't think in the case of DoubleClick it was deep enough and strong enough," he said. Google bought online ad delivery company DoubleClick for $3.1 billion in 2008. It secured unconditional clearance from EU antitrust regulators for the deal after U.S. enforcers said the deal did not pose a competitive threat in Internet advertising. Google has stepped up efforts to expand into the mobile market, responding to the trend among consumers to increasingly access the Internet from cell phones. Its Android software for smartphones is available on more than a dozen handsets from different vendors, making Google one of the companies best-positioned to challenge Apple Inc's (AAPL.O) popular iPhone, say analysts. Google, which makes 97 percent of its sales from advertising last year, has faced growing antitrust scrutiny. The European Commission, the EU antitrust watchdog, is now looking into complaints by three online companies against Google. It can fine companies up to 10 percent of their global revenues for violating EU competition rules. (Reporting by Marcin Grajewski; Writing by Foo Yun Chee; Editing by Mike Nesbit) Keywords: WPP GOOGLE/ (email@example.com; tel +32 2 287 6844; Reuters Messaging: firstname.lastname@example.org) COPYRIGHT Copyright Thomson Reuters 2010. All rights reserved.
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