HELSINKI, FINLAND: Top phone makers Nokia and Apple will seek a U.S. court hearing in a key patent battle in mid-2012, a court filing showed, raising the spectre of a prolonged legal struggle.

Handset leader Nokia sued iPhone maker Apple last October, accusing the U.S. firm of using its patented technologies without paying for them.

Nokia is seeking payment of up to 1 billion euros ($1.36 billion), analysts say.

Apple filed a countersuit in Delaware on December 11 accusing Nokia of infringing 13 Apple patents. It later removed four patents from the list.

Legal battles are increasingly common in the mobile industry as players vie for a piece of the fast-growing smartphone market.

Last week Apple sued Taiwan's HTC Corp, which makes touchscreen smartphones using Google software, accusing it of infringing 20 hardware and software patents related to the iPhone.

The U.S. International Trade Commission has agreed to investigate both companies based on each other's complaints.