Apple did not violate patents owned by Samsung in making the iPod touch, iPhone and iPad, a judge at the International Trade Commission said in a preliminary ruling on Friday.
Apple and Samsung have taken their bruising patent disputes to some 10 countries as they vie for market share in the booming mobile industry.
Apple won a landmark victory last month after a US jury found the South Korean firm had copied key features of the iPhone and awarded Apple $US1.05 billion ($A994 million) in damages.
Samsung had separately accused Apple of infringement in a complaint filed in mid-2011. It asked for the infringing products to be banned from sale in the United States.
However, ITC Judge James Gildea said on Friday that Apple did not violate the four patents in the case.
The full commission is due to decide whether to uphold or overturn its internal judge's decision in January.
"We remain confident that the full Commission will ultimately reach a final determination that affirms our position that Apple must be held accountable for free-riding on our technological innovations," Samsung said in a statement.
Apple did not immediately respond to requests for comment.
The patents in the complaint are related to 3G wireless technology, the format of data packets for high-speed transmission, and integrating functions like web surfing with mobile phone functions.
Apple has a parallel complaint filed against Samsung at the ITC, accusing Samsung, a major Apple chip provider as well as a global rival, of blatantly copying its iPhones and iPads. The ITC judge's preliminary decision is due in mid-October.
Samsung was the top-selling mobile-phone maker in the second quarter of 2012, with Apple in third place, according to data from Gartner.
Samsung's Galaxy touchscreen tablets are considered by many industry experts to be the main rival to the iPad, though they are currently a distant second to Apple's devices.
Apple has waged an international patent war since 2010 as it seeks to limit the growth of Google's Android system. The fight has embroiled Samsung, HTC and others who use Android.
Google's Android software, which Apple's late founder Steve Jobs denounced as a "stolen product", has become the world's number one smartphone operating system.
(Reporting by Diane Bartz; editing by Carol Bishopric, Gary Hill)