Taiwan's leading smartphone maker HTC has dismissed fresh patent infringement claims by US giant Apple as the legal battle between the rivals escalates.
Apple has filed a complaint against HTC with the US International Trade Commission (ITC) - which is already reviewing three other disputes between the two - over five cases linked to technology used in the iPad and iPhone.
It has also lodged a suit in a US District Court in Delaware.
"HTC is disappointed at Apple's constant attempts at litigations instead of competing fairly in the market," said HTC general counsel Grace Lei in a statement.
"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," she said.
Shares in HTC closed limit-down seven per cent at Tw$915.0 (NZ$38.6) in the Taipei bourse.
"Sentiment was hit by Apple's fresh legal action as well as heavy losses in the international and regional markets," said Alex Huang, an analyst at Mega International Investment Services.
HTC touts its own brand of smartphones and also makes handsets for a number of leading US companies, including the Nexus One unveiled by Apple rival Google.
Apple in March 2010 called on the ITC to investigate the Taiwan company over iPhone patents. That was followed months later by HTC filing for a probe into possible software patent abuse by the California-based firm.
Patent lawsuits are a regular occurrence among technology giants and Apple is currently being sued by Nokia for patent infringement. Apple has fired back a countersuit against the Finnish mobile phone giant.
And last week Apple hit back at an infringement claim by Samsung by calling for the South Korean company to be investigated.