Samsung Electronics filed its own U.S. lawsuit against Apple, accusing the iPad maker of infringing 10 patents in an escalation of the dispute over tablet and mobile technology.
The latest legal move comes after Apple sued Samsung earlier this month, claiming the Samsung's Galaxy line of mobile phones and tablets slavishly copies the iPhone and iPad.
Apple and Samsung are part of a wider web of litigation among phone makers and software firms over who owns the patents used in smartphones and tablets, as rivals aggressively rush into a market in which Apple jumpstarted with iPhone and iPad.
Samsung is one of the fastest growing smartphone makers and has emerged as Apple's strongest competitor in the booming tablet market with models in three sizes, but it remains a distant second in the space.
Samsung's Galaxy products use Google's Android operating system, which directly competes with Apple's mobile software.
Apple was Samsung's second-biggest customer last year, mostly for semiconductors. The iPhone maker's claims against Samsung focus on Galaxy's design features, such as the look of its screen icons.
The lawsuit filed by Samsung on Wednesday in a California federal court follows litigation initiated against Apple in South Korea, Japan and Germany last week.
Apple copied many of Samsung's innovations, according to Samsung's U.S. lawsuit. For instance, one of the patents Samsung accuses Apple of violating involves the ability for mobile phones to display the time, the lawsuit says.
As users travel across time zones, the ability of a mobile device to update to the local time is important for tracking appointments and meetings, the lawsuit said.
An Apple spokeswoman on Thursday referred to a previous statement from the company, which accused Samsung of blatant copying.
The case in U.S. District Court, Northern District of California is Samsung Electronics Co Ltd and Samsung Telecommunications America LLC v. Apple Inc., 11-2079.
(Reporting by Dan Levine, editing by Bernard Orr)