The EU has decided to open an in-depth probe into Google’s (NSDQ: GOOG) proposed $3.1 billion acquisition of DoubleClick, reports Reuters, citing a source familiar with the situation. On October 22, the EU said that its first inquiry had been extended to today, November 13, from the original October 26 deadline, “so proposed remedies to possible competition problems could be tested.” If the reports are true, it means the EU still remains unsatisfied with Google’s concessions and the competitive implications of the deal. Reuters (NSDQ: RTRSY) notes that in-depth probe would last at least 90 days, but doesn’t in itself imply that new concessions will be required. Meanwhile, the FTC has its own investigation into the deal, which has yet to be resolved.

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Update: The EU has confirmed the initial reports: “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 Commission has 90 working days (until 2 April 2008) to take a final decision on whether the proposed transaction would significantly impede effective competition within the European Economic Area (EEA) or any substantial part of it. The decision to open an in-depth inquiry does not prejudge the final result of the investigation.” Read more in the full statement.