SAN FRANCISCO - It took almost two months, but on Friday Apple Inc. responded to a patent-infringement lawsuit with one of its own against the Finnish mobile-phone giant Nokia Corp.

Apple said it filed suit against Nokia, charging that company with violating 13 of its patents.

In a statement, General Counsel Bruce Sewell said: "Other companies must compete with us by inventing their own technologies, not just by stealing ours."

The company said it was responding to a lawsuit that Nokia filed against Apple on Oct. 22. That suit, at its heart, was all about the iPhone.

In its suit, filed in the U.S. District Court for the District of Delaware, Apple denies any infringement of patents listed in Nokia's original suit, argues that Nokia's patents are not essential to any wireless-technology standards and that Nokia, in dealing with Apple, "has sought to gain an unjust competitive advantage over Apple by charging unwarranted fees to use patents that allegedly cover industry compatibility standards."

Apple is asking the court to dismiss Nokia's complaints and enter a judgment in favor of Apple in which Nokia would be declared in breach of contract regarding the use of its wireless technology.

Nokia's own litigation against Apple covered 10 of the company's wireless-technology patents, which Nokia said Apple's iPhone has infringed upon since the device hit the market in 2007.

Nokia claimed the patents in question "relate to technologies fundamental to making devices," and which are compatible with the GSM and UMTS or 3G WCDMA, as well as wireless standards for local networks.

"This certainly could drag on for a while," said Barry Cohen, a partner and intellectual-property specialist with the Philadelphia law firm Thorp, Reed & Armstrong. "The biggest issue is going to be what to do with the 13 patents Nokia is accused of violating."

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