Apple Inc won a preliminary ruling from a U.S. trade panel that Taiwanese handset maker HTC Corp infringed on two of the California company's patents.
HTC, which uses Google's Android operating system for its smartphones, said it would vigorously fight the infringement finding.
An International Trade Commission judge on Friday made the ruling, but the full commission must now rule on whether it will uphold or reverse its administrative judge's decision.
The ruling, though preliminary, will be closely dissected as it is one of the first between Apple and other smartphone makers that use Android.
Smartphone technology has spawned a wealth of patent litigation. Apple also has filed complaints against Samsung Electronics, which also uses the Android software platform. Apple recently settled a case against Nokia.
Microsoft and Motorola also have filed smartphone related lawsuits against each other.
Android-based smartphones have outpaced iPhones globally but Apple is gearing up to launch a new iPhone this year, which is likely to give it a big boost.
Apple initially accused HTC of infringing 10 patents but six were dropped from the case for various reasons. The ITC judge ruled that HTC infringed two of the remaining four.
A final determination in the case is due on December 6.
Apple filed a parallel lawsuit against HTC in a court in the U.S. District Court in Delaware.
Asked for comment, Apple reiterated a previous statement by Chief Executive Officer Steve Jobs that competitors should create their own original technology, not steal ours.
The ITC is a popular venue for patent disputes because it can bar the importation of devices made with infringing technology. Often parallel lawsuits are filed in district courts to try to recoup any financial damages.
We are confident we have a strong case for the ITC appeals process and are fully prepared to defend ourselves using all means possible, said HTC General Counsel Grace Lei in an email statement.