The European Commission opened a four-month, in-depth review on Tuesday of Google Inc's plans to buy rival DoubleClick for $3.1 billion.

"The Commission's initial market investigation indicated that the proposed merger would raise competition concerns in the markets for intermediation and ad serving in online advertising," the European Union's top competition regulator said in a statement, confirming what a source familiar with the situation had earlier told Reuters.

The Commission has 90 working days, until April 2, to take a final decision on whether the proposed transaction would significantly impede effective competition.

Google DoubleClick Deal In Four-Month In-Depth Review By EU [uk.reuters.com]