July 10 (Bloomberg) -- Qualcomm Inc., the second-largest maker of computer chips for mobile phones, said U.S. regulators are probing whether Finland's Nokia Oyj is violating trade rules by importing cellular telephones that infringe Qualcomm patents. The U.S. International Trade Commission started an investigation July 7, Qualcomm said today in a statement. The San Diego-based company asked the agency June 9 to bar the importation of infringing Nokia devices. Qualcomm has filed lawsuits in the U.S. and U.K. claiming Nokia, the world's biggest maker of cell phones, is using its technology without permission. The company is stepping up legal actions as demand soars for computer chips allowing phones to surf the Internet, take photos or watch videos. ``Filing a case with the ITC has real advantages for plaintiffs,'' said Robert Yoches, a patent lawyer with Finnegan Henderson Farabow Garrett & Dunner in Washington.