UPDATE 2-AU Optronics hits Samsung with patent countersuit
* AU Optronics sues Samsung over flat-screen patents
* Lawsuit follows Samsung complaint against AU (Adds Samsung comment in paragraph five, Best Buy declining to comment)
WILMINGTON, Del., June 28 (Reuters) - AU Optronics Corp (2409.TW) of Taiwan hit Korea's Samsung Electronics Co Ltd (005930.KS) with a countersuit for patent infringement, ratcheting up their dispute over flat panel technology.
AU Optronics also sued AT&T (T.N), Best Buy Co Inc (BBY.N) and BrandsMart U.S.A. Inc, accusing them of selling or distributing infringing technology used in televisions, monitors, laptops, mobile phones and tablet computers.
The lawsuit, filed on Monday in Delaware District Court, seeks an order to stop the alleged infringement as well as monetary damages. AU Optronics, the world's No 4 maker of flat screens, asked the court to treble any monetary award because the infringement was willful.
Earlier this month, Samsung filed a complaint against AU Optronics with the International Trade Commission and in federal court for patent infringement related to flat screens.
"Samsung Electronics is committed to respecting the intellectual property rights of others," the Korean company said in a statement. "However, we will also work actively to protect our rights and our customers when another party makes unsubstantiated infringement claims against Samsung."
Samsung vies for the top flat-screen position with Korean rival LG Display Co Ltd (034220.KS).
AT&T spokesman Mark Siegel said the company had not reviewed the lawsuit and declined to comment. Best Buy declined to comment and BrandsMart did not reply to a request for comment.
The case is AU Optronics Corp v Samsung Electronics Co Ltd, U.S. District Court, District of Delaware, No. 11-568. (Reporting by Tom Hals; editing by John Wallace and Robert MacMillan)