Smartphone maker HTC has hit back, after being sued by Apple not once but twice, claiming the patents Apple has accused it of infringing are invalid.

Legal-focused site Groklaw notes case, Apple Inc. vs High Tech Computer Corp. et al, is now before the US District Court in Delaware.

According to court papers the case highlights: "The Asserted Patents cover generally various software and/or hardware technologies that can be incorporated into mobile communication devices, including cellular phones and smart phones, among various other types of products."

In response, HTC denies patent infringements, stating: "Four of the patents are invalid for "failure to comply with one or more of the conditions for patentability set forth in Title 35 of the United States Code, including, but not limited to, utility, novelty, non-obviousness, enablement, written description and definiteness in accordance with 35 U.S.C. §§ 101, 102, 103, 112, and/or 116, or are invalid pursuant to the judicial doctrine barring double-patenting.

Groklaw adds: "HTC also claims prior art, marking, laches and marking defences, and it says it has license agreements with third party suppliers to do what they do the things Apple is suing them over. It asks the court to declare the patents invalid. Here's a recent case highlighted on EFF's site where some of those types of defences worked perfectly."

Meanwhile, Apple is asking that all four current cases involving these patents be consolidated, suggesting: "Consolidation is appropriate in this instance because the four cases involve numerous common issues of law and fact, including eleven patents that Apple has asserted against both Nokia and HTC."

"Given the overlapping patents and technologies at issue in the cases, consolidation offers the benefit of conserving resources and promoting judicial economy by avoiding the need for duplicative discovery or any other redundant litigation activities, such as multiple Markman hearings concerning the same patents. Importantly, consolidation before a single judge will also ensure that there are no inconsistent pretrial rulings- most notably inconsistent constructions of claim terms in the eleven overlapping patents."

Additionally, Apple has asked for the case to be moved from Delaware to Northern California. Groklaw anticipates HTC to fight hard and long in its legal battle with Apple following its affirmative defences and counterclaims.