Responding to a lawsuit brought against the company by Nokia, Apple on Friday filed a countersuit claiming that Nokia is infringing 13 Apple patents. "Other companies must compete with us by inventing their own technologies, not just by stealing ours," said Bruce Sewell, Apple?s General Counsel and senior vice president.

Apple's lawsuit claims Nokia is infringing on 13 of Apple's patents, and says Nokia chose to "copy the iPhone," especially its user interface, to make up for its declining share of the high-end phone market.

Nokia's lawsuit, filed in October, claims that Apple infringes on 10 of its patents covering both phone calls and Wi-Fi access.

The ten patents in suit relate to technologies fundamental to making devices which are compatible with one or more of the GSM, UMTS (3G WCDMA) and wireless LAN standards. The patents cover wireless data, speech coding, security and encryption and are infringed by all Apple iPhone models shipped since the iPhone was introduced in 2007.

In its court filing, Nokia had made various offers to Apple for a license agreement, which Apple rejected.

Both suits were filed in federal court in Delaware.