Nokia, the world's top handset maker, has broadened its patent fight with Apple Inc to include the iPad, deepening the bitter legal disputes between the two smartphone rivals.

The firms turned to the courts in the last year as Nokia battles Apple, which only entered the cellphone business in 2007, but has taken a sizeable share of the fat-margined, fast-growing smartphone market.

The Finnish firm, on the other hand, has shed market share in smartphones along with margins and stunned investors last month by delaying its new software upgrade for phones, seen as key in its struggle with Apple.

Nokia filed a complaint in the Federal District Court in the Western District of Wisconsin, alleging Apple's iPhone and iPad 3G products infringe five of its patents.

"Apple is continuing to seek a free ride on the back of Nokia patents," said a Nokia spokesman.

The patents have not been covered in Nokia's previous legal actions against Apple, and relate to antenna technologies, technologies for enhanced speech and data transmission, and to using positioning data in applications.

"By moving the litigation to another state Nokia is making another move in the complex game of intellectual property chess it is playing with Apple," said Ben Wood, research director at CCS Insight.

"On this occasion it is interesting to see it choosing patent areas such as antenna design where it has developed competence over many years," Wood said.