AMSTERDAM (AP) — Europe's top regulator has warned Nokia not to try to become a "patent troll" after the Finnish company sold most of its cellphone-making business to Microsoft Corp. this year but retained its patent portfolio.

Joaquin Almunia said in a speech in Paris on Monday he had approved the $7.2 billion sale as not presenting problems on Microsoft's side, but there is a danger Nokia will now attempt to "extract higher returns" from its patent portfolio. "In other words...behave like a patent troll, or to use a more polite phrase, a patent assertion entity."

Almunia, in charge of competition at the European Commission, the executive arm of the European Union, warned he will open an antitrust case against the company if it attempts to take "illegal advantage" of its patents.