Menlo Park, Calif.—Google Inc. has issued a warning to agencies, advertisers and publishers that attempt to place native ads on its Google News site: Don't. In a blog post about native ads, which look like surrounding journalistic content but are actually sponsored by advertisers, Google said: “It's difficult to be trusted when one is being paid by the subject of an article. ... Google News is not a marketing service, and we consider articles that employ these types of promotional tactics to be in violation of our quality guidelines.” Google urged sites to separate advertorial content from other materials and block it from being included on Google News. If sites violate its guidelines, Google said, it may remove articles or even entire publications from Google News.