Apple said Friday that it filed a countersuit against Nokia, charging the Finnish phone maker with infringing on 13 of its patents.

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

In papers filed in U.S. District Court of Delaware, Apple accused Nokia of purloining technologies that govern real-time signal processing, teleconferencing, display graphics, power conservation, and other areas related to smartphones.

"Nokia needs access to Apple's intellectual property because Nokia has copied and is now using that patented technology," Apple said in its filing. "Nokia chose to copy the iPhone, especially its enormously popular and patented design and user interface," Apple alleged.

Apple named the Nokia E71 as one of the products that allegedly infringe its patents, as well as all Nokia devices that have a built-in camera and those that use the S60 or Symbian platforms. The E71 is a high-end Nokia smartphone that currently has a street value of about $250.

Apple is asking a judge to award unspecified damages and to prohibit Nokia from using the technologies in question in its products.

Nokia originally filed suit against Apple in October, charging the Mac manufacturer with stepping on 10 of its patents related to wireless technology used in the iPhone.

Nokia isn't Apple's only courtroom combatant of late. The company is involved in an ongoing copyright battle with Mac cloner Psystar. Psystar recently halted its sales of Mac clones after the judge overseeing the case ruled in favor of Apple on most counts. Psystar agreed to pay Apple $2.7 million.

Apple shares were off 1.16%, to $194.16, in midday NASDAQ trading Friday.