BlackBerry-maker Research In Motion has sued Motorola, over what the Canadian company says are patent infringements and "exorbitant" licensing fees, according to court documents. The civil action, filed on Friday in U.S. District Court for the Northern District of Texas, alleges that Motorola infringed on a number of patents held by RIM.

In addition, RIM alleges 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 telephone handset users to use Wi-Fi, RIM said.

At the same time, Motorola is refusing to acknowledge or pay royalties for certain patents held by RIM, the BlackBerry-maker said.

RIM claims that Motorola's response to the "declining fortunes" of its own handset business can been seen in dramatic increases in royalties charged to RIM. None of the allegations has been proved in court.

RIM's worldwide subscriber base of about 12 million includes business executives, politicians and professionals who rely on the BlackBerry to send secure e-mails. BlackBerry has been expanding from its mainstay enterprise market into the consumer sector with sleeker handsets that offer a range of services in addition to e-mail.