BlackBerry-maker Research In Motion and its rival Motorola are sueing each other over alleged patent infringements for technology used in their mobile phones.

RIM, which is a Canadian company, has filed its case in US District Court for the Northern District of Texas and claims not only that Motorola is infringing several of its patents but is also demanding "exorbitant" licensing fees.

Reuters reports that RIM is alleging that Motorola "is demanding exorbitant royalties ... for patents that Motorola claims are essential to various standards for mobile wireless telecommunications and wireless computing that RIM practices".

This includes technology that allows mobile phone handset users to use Wi-Fi, RIM said.

RIM's lawsuit claims that Motorola's response to the "declining fortunes" of its handset business can been seen in dramatic increases in royalties being charged to RIM for patented technologies.

RIM also says that Motorola is not paying royalties for, or indeed even acknowledging, its use of patented technologies owned by RIM.

Motorola is denying RIM's claims and has countersued with two lawsuits in Texas and Delaware.

Motorola is challenging RIM's patents and is arguing also that RIM is infringing on certain Motorola patents.

RIM products targeted in one of the Motorola lawsuits include the BlackBerry 8100, 8300 and 8800 models and BlackBerry Exchange Server software.

In a statement sent to Reuters, Motorola said: "We have not yet reviewed the complaint, but based on our understanding of the matter, we believe that their claims are entirely without merit and Motorola intends to vigorously defend itself".

Reuters adds that this dispute goes way back to 2003 when the two rivals failed to reach an amicable renewal of a 2003 cross-license agreement.