BlackBerry Ltd's patent claims related to an attachable keyboard accessory for Apple Inc's iPhones don't comply with legal requirements for patentability, Typo Products LLC said in a court filing late on Tuesday.

BlackBerry sued Typo last month, saying its physical keyboard that can be attached to some of Apple's iPhone models infringes patents.

The Canadian smartphone maker claimed that Typo's keyboard infringes its design and alleged that the startup's $99 keyboard featuring angled miniature keys is similar to those on many BlackBerry devices.

In a request to a federal court in San Francisco, Typo asked a US judge to rule that the patents have not been infringed and to declare some of the claims invalid and unenforceable.

Typo said that one of the patents is not enforceable because the design was widely available for sale in 1988, prior to the BlackBerry patent approval, and this was not disclosed to the US Patent and Trademark Office.

Typo urged the judge to dismiss every claim in BlackBerry's complaint with prejudice and not be subject to further action, the filing showed.

Typo, founded by "American Idol" co-host Ryan Seacrest, also asked the court for a permanent injunction to prevent BlackBerry from suing or threatening to sue the company for patent infringement.

BlackBerry, a once dominant smartphone maker has lost market share to the iPhone and other touchscreen devices.

Typo Products is named after the typographical errors that people make while typing on smartphones, according to its website.

BlackBerry posted billions in losses in recent quarters as its latest devices sold poorly, but it has maintained a loyal niche of customers who prefer to type on a physical keyboard.

The case is BlackBerry Ltd v. Typo Products LLC, case no. 3:14-cv-23 in the United States District Court for the northern district of California.