Aug 13 (Reuters) - A U.S. trade judge ruled on Friday that Alphabet Inc"s (GOOGL.O) Google infringed five patents belonging to Sonos Inc (SONO.O) that concern smart speakers and related technology, a decision that could lead to an import ban. The brief ruling from Charles Bullock, the chief administrative law judge of the U.S. International Trade Commission, did not explain why Google"s sale of the products violated a 1930 federal tariff law, commonly known as Smoot-Hawley, designed to prevent unfair competition. Sonos has been trying to block Google from importing Home smart speakers, Pixel phones and other products from China. Google did not immediately respond to requests for comment. Sonos said it was pleased with the preliminary ruling, which it said "confirmed Google"s blatant infringement" and furthered its efforts to defend its technology against alleged misappropriation by larger rivals. Shares of Sonos were up 11.4% in after-hours trading. Friday"s ruling is subject to review by the full ITC, scheduled for Dec. 13 according to the commission"s website. The ITC case is part of an array of litigation between the two companies, including cases in California, Texas, France, Germany and the Netherlands, according to regulatory filings. Google has said Sonos repeatedly sought help during their years of partnership, and it eventually integrated Sonos products into its Play Music service and Google Assistant software. Some Sonos speakers have used voice assistance technology from Google and Amazon.com Inc (AMZN.O). Google"s own Nest smart speakers include Google Assistant technology. Sonos is based in Santa Barbara, California, and Alphabet in Mountain View, California.