SAN FRANCISCO (Reuters) - Google Inc on Thursday accused Microsoft Corp and Nokia of conspiring to use their patents against smartphone industry rivals, and said it has filed a formal complaint with the European Commission.

In its complaint, Google claimed Microsoft and Nokia, which cooperate on smartphone technology and production, transferred 1,200 patents for assertion to a group called MOSAID, which the company called a "patent troll" -- a term referring to a holder of patents that litigates them aggressively.

"Nokia and Microsoft are colluding to raise the costs of mobile devices for consumers, creating patent trolls that side-step promises both companies have made," the Internet search leader said in a statement. "They should be held accountable, and we hope our complaint spurs others to look into these practices."

Nokia and Microsoft were not immediately available for comment.

(Reporting by Edwin Chan; Editing by Gary Hill)