The fight is related to Apple's war against Google, whose Android software powers many of Samsung's devices.

Samsung said in a filing late Monday that examiners at the U.S. Patent and Trademark Office (PTO) had taken a second look at an Apple patent and decided that it should not have been granted. The patent allows a user with a touch screen to bounce back to the image on the screen if the user goes beyond the edge.

The patent was one of six that Samsung was found to have infringed by a jury in a California federal court in August. It awarded Apple $1.05 billion in damages.

The case is being appealed, and Samsung is pursuing other challenges such as requests for the PTO to reexamine the patent.

Scott Daniels, a litigation partner at Westerman, Hattori, Daniels & Adrian LLP who is not part of the case, said the PTO's preliminary invalidation is not the end of the battle over this specific patent.

He said the patent remains valid through the appeals process.

The case in U.S. District Court, Northern District of California, is Apple Inc v. Samsung Electronics Co Ltd et al, No. 11-1846.

(Reporting By Diane Bartz;editing by Sofina Mirza-Reid)

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