Finnish mobile maker Nokia has filed two new patent infringement lawsuits against Taiwanese smartphone maker HTC in the USA.
The lawsuits were filed in the US International Trade Commission and the US district court of Southern California.
Both the lawsuits cover nine Nokia patents, which are alleged to have been infringed by HTC.
Nokia said it started actions against HTC in 2012 to end the unauthorised use of its innovations and technologies.
"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," the company said.
"We have, therefore, taken these further steps to hold HTC accountable for its actions."
HTC said: "Upon receiving the official document, HTC is to consider all legal options to protect our rights."
Last month, the Amsterdam district court in the Netherlands granted a preliminary injunction to Nokia, which will prevent HTC from using microphone parts made by STMicroelectronics in its HTC One phones.
Earlier this year, Nokia also won a patent infringement case against HTC in Germany related to power-saving technology.
