By Inti Landauro

PARIS--France's anti-trust regulator said Wednesday it has opened an in-depth probe into the acquisition of the SFR mobile telephone company by French cable TV operator Numericable Group SA (NUM.FR).

"The authority considers the operation raises serious doubt about possible obstacles to free competition and requires the opening of an in-depth probe (phase 2)," a statement on its website said.

The phase 2 probe includes questioning all market players as well as other local institutions about the deal. The probe can last for up to 65 working days but may be extended.

The board of French telecom-to-media group Vivendi SA (VIV.FR) in April accepted an offer for SFR from Numericable valuing the company at 17 billion euros ($22.83 billion). The transaction is conditional on the approval of all French regulators.

Numericable is a unit of Altice SA (ATC.AE).

Write to Inti Landauro at inti.landauro@wsj.com

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