Google’s ambitions in the online advertising business suffered a potential setback on Tuesday as the European Commission said it was opening an in-depth review of the internet company’s proposed $3.1bn takeover of DoubleClick.

In a statement, the Commission said an initial market investigation had indicated “that the proposed merger would raise competition concerns in the markets for intermediation and ad-serving in online advertising”. It now has until April 2 next year to reach a final decision.