Motorola's handset division has slapped Microsoft with a patent infringement lawsuit just two days after Microsoft accused Motorola of inflating royalties on networking technology used in Microsoft's Xbox.

In complaints filed with the U.S. District Courts for the Southern District of Florida and the Western District of Wisconsin, Motorola Mobility alleges that Microsoft is infringing on 16 of its patents on its PC and server software, Windows Mobile platform and Xbox products.  

"We are committed to protecting the interests of our shareholders, customers and other stakeholders and are bringing this action against Microsoft in order to halt its infringement of key Motorola patents," said Kirk Dailey, corporate vice president of intellectual property at Motorola Mobility. "Motorola has invested billions of dollars in R&D to create a deep and broad intellectual property portfolio, and we will continue to do what is necessary to protect our proprietary technology."

The patents cover a range of technologies, including digital video coding, instant messaging and graphical passwords. Motorola Mobility wants the courts to order Microsoft to stop using its patented technology and provide compensation for past patent violations.

The suit over royalties is the second Microsoft has filed against Motorola. In October, Microsoft sued Motorola over nine patents used in Motorola's Android-based smartphones.

"It is unfortunate that Microsoft has chosen the litigation path rather than entering into comprehensive licensing negotiations, as Motorola has mutually beneficial licensing relationships with the great majority of technology companies industry-wide," Dailey said.

Horacio Gutierrez, Microsoft's deputy general counsel of intellectual property and licensing, said that Motorola's lawsuit was "typical of the litigation process."

"We remain confident in our position and will continue to move forward with the complaints we initiated against Motorola in the U.S. District Court for the Western District of Washington and with the International Trade Commission," he said.