San Francisco, Dec 12 (DPA) Apple has sued Nokia for allegedly infringing on 13 patents, less than two months after the Finnish cellphone giant charged in a lawsuit that Apple's iPhone violated 10 of its patents.

The counter suit Friday claimed that Nokia was attempting to copy the iPhone and its heralded user interface to help it stem Apple's lead in the market for smartphones.

"Other companies must compete with us by inventing their own technologies, not just by stealing ours," said Bruce Sewell, Apple's general counsel, in a statement.

The patents Apple alleges Nokia is infringing deal with, among other things: Connecting a phone to a computer, teleconferencing, menus on a touch screen, power conservation in chips, and "pattern and color abstraction in a graphical user interface". The company also denies Nokia's claims of patent infringement.

Nokia sued Apple in late October claiming that Apple infringed on patents covering wireless data, speech coding, security and encryption. Nokia said it had signed licenses with other companies that allowed them to use the technology that Apple was using in all its iPhones.

"The basic principle in the mobile industry is that those companies who contribute technology development to establish standards create intellectual property, which others then need to compensate for," said Ikka Rahnasto, vice president of legal and intellectual property at Nokia, in a prepared statement.

"By refusing to agree to appropriate terms for Nokia's intellectual property, Apple is attempting to get a free ride on the back of Nokia's innovation," Rahnasto said.

The lawsuits in a federal court in Delaware come as Nokia tries to retain its status as the world's largest maker of cellphones, and as its market share in the profitable smartphone sector shrinks in the face of competition from the iPhone and other challengers.