The world's biggest mobile phone maker, Nokia, has filed a lawsuit against Apple claiming the iPad 3G and iPhone infringe five of its patents. Nokia claims the infringements involve technology used to enhance speech and data transmission and antenna innovations for compact devices. This is the latest salvo in a long-running legal battle between the two companies. Nokia and Apple are embroiled in another dispute concerning the iPhone. "We've taken this step to protect the results of our pioneering development and to put an end to continued unlawful use of Nokia's innovation," said Paul Melin, general manager of patent licensing at Nokia. In a statement, the company said that during the past two decades Nokia has invested about $51bn (£34bn) in research and development and has rounded up 11,000 patents. Last year Nokia filed a similar lawsuit which claimed that various Apple products infringed Nokia patents. Apple responded with a countersuit against Nokia for infringing Apple patents with its smartphones. Meanwhile, Apple is also involved in another legal row with Taiwan's HTC, maker of Google's Nexus One phone, which it says has infringed patented technology. Patent disputes are common in the technology industry and often end with some kind of licensing agreement, correspondents say. The Nokia lawsuit came on the day Apple announced that its iPad tablet computer will go on sale in nine countries outside the US on 28 May. Source: BBC