HTC was the first company to manufacture a cell phone based on Google Inc.'s Android operating system, which has emerged as a significant competitor to the iPhone. It is also making the Nexus One phone, which Google is selling directly to consumers.

Apple said HTC has infringed on 20 of its patents covering aspects of the iPhone's user interface and hardware.

"We can sit by and watch competitors steal our patented inventions, or we can do something about it," Apple CEO Steve Jobs said in a statement. "We've decided to do something about it." When the iPhone first came out in 2007, it changed the smart phone landscape by introducing a stylish, easy-to-use device. Apple later followed with an application store that extended the capabilities of the device far beyond just making phone calls, checking e-mails and surfing the Web.

Since the iPhone's debut, Apple has had a lock on much of the smart phone market, alongside Research In Motion Ltd., which makes the popular BlackBerry devices.

However, over the last year or so, more competition has emerged from such phone makers as HTC and Motorola Inc., which are rolling out smart phones that use Google's Android software. Not only do these phones appeal to consumers, but they also work on numerous wireless networks, unlike the iPhone, which is still limited in the US to AT&T Inc.

In a court filing, Apple said that a bevy of HTC-made cell phones - including the Nexus One and T-Mobile's G-1 and the myTouch 3G - are using patent-protected technologies owned by Apple without having a license for them.