Nokia has announced it is suing Apple in German and US courts for patent infringement, claiming the US tech giant was using its technology in "many" products without paying for it.
Finnish Nokia, once the world's top mobile phone maker, said the two companies had signed a licensing agreement in 2011, and since then "Apple has declined subsequent offers made by Nokia to license other of its patented inventions which are used by many of Apple's products".
"After several years of negotiations trying to reach agreement to cover Apple's use of these patents, we are now taking action to defend our rights," Ilkka Rahnasto, head of Nokia's patent business, said in a statement.
The complaints, filed in three German cities and a district court in Texas, concern 32 patents for innovations related to displays, user interface, software, antennae, chipsets and video coding. Nokia said it was preparing further legal action elsewhere.
Nokia was the world's leading mobile phone maker from 1998 until 2011 when it bet on Microsoft's Windows mobile platform, which proved to be a flop. Analysts say the company failed to grasp the growing importance of smartphone apps compared to hardware.
It sold its unprofitable handset unit in 2014 for some $7.2bn to Microsoft, which dropped the Nokia name from its Lumia smartphone handsets.
Meanwhile Nokia has concentrated on developing its mobile network equipment business by acquiring its French-American rival Alcatel-Lucent.
Including its 2013 full acquisition of joint venture Nokia Siemens Networks, Nokia said the three companies united represent more than €115bn of R&D investment, with a massive portfolio of tens of thousands of patents.
The 2011 licensing deal followed years of clashes with Apple, which has also sparred with main rival Samsung over patent claims.
At the time, Apple cut the deal to settle 46 separate complaints Nokia had lodged against it for violation of intellectual property.