Nokia recently filed fresh patent infringement complaints with the U.S. International Trade Commission against HTC. The company said its two complaints with the ITC now cover nine different patents, and also noted that it now has a total of 50 patents asserted against HTC around the world.

The Finnish phone maker said the patents are related to "enhanced speech and data transmission, efficient component layout in compact unibody designs and worldwide roaming capability, as well as to enhance software features including application data sharing between phones, permissions management in applications, video encoding and decoding, and expanding a device's capabilities with new applications."

"We began actions against HTC in 2012 to end the unauthorized use of our proprietary innovations and technologies," Nokia said in a statement provided to AllThingsD. "Since then, despite the German courts confirming infringements of Nokia patents in HTC products, HTC has shown no intention to end its practices, instead it has tried to shift responsibility to its suppliers. We have therefore taken these further steps to hold HTC accountable for its actions."

Reached for comment by TechnoBuffalo, an HTC spokesperson said: "Upon receiving the official document, HTC is to consider all legal options to protect our rights."

HTC is also facing criticism in the media following the recent departure of several executives, moves that raised questions about management within the firm and it's ability to compete against its biggest rivals, Samsung and Apple.