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The Taiwanese smartphone maker HTC has filed a lawsuit in the US against Apple, accusing its American rival of infringing its patents.

HTC is trying to stop US imports of iPhones, iPads, iPods and Mac computers.

It is the latest step in a legal battle over patents between the two companies.

The battle for sales of smartphones took a new twist on Monday when Google agreed to pay $12.5 billion to buy Motorola's mobile unit.

Google wants to move ahead with development of its Android system for mobile telephones, making it more competitive with rivals like Microsoft.

The legal battle over patents between HTC of Taiwan and Apple in the US is part of the sales war.

HTC General Counsel Grace Lei said in a statement: "We are taking this action against Apple to protect our intellectual property, our industry partners, and most importantly our customers that use HTC products."

Apple has not responded to requests for comment from the 91Èȱ¬.

In July, HTC was found to infringe two iPhone patents in a case brought by Apple at the US International Trade Commission (ITC).

However HTC, which is one of the world's fastest-growing smartphone makers, has vowed to appeal against the ruling, which threatens its business model of designing products around the Android operating system.

Google's acquisition of Motorola Mobility (MMI) may offer a greater degree of protection to Android handset makers.

"MMI's patent portfolio is likely to help Google protect manufacturers using the Android ecosystem against litigation from Apple and Microsoft," Bernstein Research said in a note to clients.

Motorola, Nokia, HTC, Apple, Google and Samsung are all involved in one or more patent lawsuits.