The European Commission (EC) is to undertake an in-depth investigation into Telefonica’s proposed €8.6 billion takeover of E-Plus, KPN’s German unit.

It will also boot out a request from Germany’s regulator to lead the probe, said Reuters’ sources.

Bundeskartellamt, Germany’s trustbuster, had previously asked the EC to take a lead role in scrutinising Telefonica’s takeover of E-Plus, which would see the number of mobile network operators in Germany reduced from four to three

“The merger exclusively affects the German mobile communications markets,” said the anti-trust regulator in a statement quoted by Reuters. “A referral of the case to the Bundeskartellamt would thus be the right approach.”

These arguments, however, have apparently failed to persuade the EC.

A formal EC decision on how the investigation into the German merger should proceed is slated for 20 December.