Apple's launched a new series of patent infringement claims against HTC, relating to several Android smartphones and the company's Flyer tablet.
It says the products violate five of its patents, including three which are the subject of a patent dispute with Samsung, relating to scrolling, programmable tactile touch-screen displays, and a double-sided touch-sensitive panel.
It's also claiming infringement of patents for scrolling, zooming and rotating content on a screen, and one covering 'portable computers'.
It filed its complaint yesterday with the International Trade Commission, which is already examining three other patent disputes between the companies, and has also filed suit in a Delaware district court.
But HTC says the claims are groundless, and accuses Apple of being too keen to resort to the courts.
"HTC is disappointed at Apple's constant attempts at litigations instead of competing fairly in the market," says general counsel Grace Lei.
"HTC strongly denies all infringement claims raised by Apple in the past and present and reiterates our determination and commitment to protect our intellectual property rights."
Apple made its first complaints against HTC in March last year, claiming it had violated a number of iPhone patents. HTC retaliated later in the year, accusing Apple of violating its software patents.
And Apple may be about to lose one of its most senior patent lawyers, according to Reuter. It says the company's chief IP counsel, Richard "Chip" Lutton Junior, will be leaving in the next month. It doesn't suggest why.