NTP, a patent-holding firm which won a $600 million settlement from Blackberry maker Research in Motion, now has Apple, Google, HTC Corp., LG Electronics, Microsoft and Motorola in its sights.

The Richmond, Virginia-based NTP filed lawsuits against the six technology giants, accusing them of infringing its wireless e-mail patents in mobile phones.

NTP, in the suits filed in the US District Court for the Eastern District of Virginia, accused the companies of infringing eight patents it holds for wireless e-mail.

"Use of NTP's intellectual property without a licence is just plain unfair to NTP and its licencees," NTP co-founder Donald Stout said in a statement.

He said legal action "is necessary to ensure that those companies who are infringing NTP's patents will be required to pay a licencing fee."

NTP describes its other co-founder, the late Thomas Campana, as the "inventor of wireless e-mail." In 2006, Canada's Research in Motion, maker of the Blackberry, agreed to pay 612 million dollars to NTP to settle patent infringement claims and to licence NTP-patented technology.

NTP has separately filed suits against mobile phone manufacturer Palm and several telecom companies accusing them of patent infringement. Those cases, launched in 2006, are ongoing.

NTP has a licencing agreement with Nokia and the Finnish mobile phone giant was not named in the suits. Patent lawsuits are a regular occurrence among technology giants and Apple is currently being sued by Nokia for patent infringement. Apple has fired back a countersuit against Nokia.

Taiwan's HTC and Apple are also currently suing each other over patent claims.

Analyst Jon Ogg of said the latest NTP lawsuit could prove to be good news for RIM.