US patent authorities rejected Apple's key "pinch-to-zoom" patent in an initial ruling, the second setback in less than two months for the iPhone maker in its patent battle with Samsung Electronics.
Apple's shares have taken a beating recently, with investors worried about rising competition from Samsung and other mobile device makers using Google's Android platform.
Apple scored a sweeping legal victory over its South Korean competitor in August when a US jury found Samsung had copied critical features of the hugely popular iPhone and iPad and awarded Apple US$1.05 billion (A$1 billion) in damages.
Samsung and Apple, the world's top two smartphone makers, are locked in patent disputes in at least 10 countries as they vie to dominate the lucrative mobile market and win over customers with their latest gadgets.
The US Patent and Trademark Office on Wednesday temporarily invalidated the "pinch-to-zoom" patent, which had been contested at the trial in August. The jury had ruled that Samsung had infringed six of seven Apple patents.
The "pinch-to-zoom" feature distinguishes between single-touch and multitouch gestures on a mobile device screen and allows the user to zoom in or out by moving two fingers apart or closer together while touching the display.
A US judge denied on Monday Apple's request for a permanent injunction against Samsung's smartphones.
Samsung won a preliminary invalidation of Apple's "rubber-banding" patent in October that had the "bounce" feature. 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.
When the US patent office rules against a patent, the full process involves multiple steps and can take years. It can also often be appealed in court, further tying up the process.
The ruling by the US patent office after Samsung requested an examination of the patent was included in documents filed by Samsung in a federal court in San Jose, California.
Apple's claims were rejected on the grounds that prior patents covered the inventions.
Representatives for Apple and Samsung were not immediately available for comment.
A Dutch court ruled in October that Samsung did not infringe on Apple's patent by using certain multi-touch techniques on some of the Samsung Galaxy smartphones and tablet computers.
(Reporting by Balaji Sridharan and Sayantani Ghosh in Bangalore; Editing by Edwina Gibbs and Don Sebastian)