Samsung's high-stakes legal battle with Apple was bolstered Tuesday by word that the US Patent and Trademark Office was second-guessing a patent at issue in the case.

Officials re-examined an Apple patent for an effect that makes a smartphone screen appear to "bounce" when an edge is tugged by a finger and tentatively concluded it should be invalidated because it was not new, intellectual property analyst Florian Mueller reported at FossPatents.com.

"Apple's rubber-banding (overscroll-bounce) patent is still going to go through a lengthy process before it may or may not be invalidated," Mueller said in a blog post.

The tentative decision by the patent office could be used by Samsung to petition US District Court Judge Lucy Koh to override part of a jury verdict that called for the South Korean company to pay Apple $1.05 billion in damages.

The patent was one of a half-dozen at the heart of a massive clash between the US and South Korean electronics giants in federal court in California.

Apple is seeking to ban various Samsung phones and tablets on the basis of that verdict in Koh's courtroom.