SEOUL, South Korea - Samsung Electronics Co. said Thursday it filed a complaint with American authorities over alleged unfair trade practices by Japanese rival Sharp Corp., fueling an intensifying legal battle over flat panel technology.

Samsung said in a statement that it filed the complaint with the United States International Trade Commission on Dec. 21, claiming that Sharp and two U.S. subsidiaries imported and sold liquid crystal display products that infringe on four of Samsung's U.S. patents.

The complaint came after Sharp earlier this month sued Samsung in a South Korean court, also alleging patent violations for LCDs. It demanded damages and a halt to manufacturing and sales of affected TVs and display panels.

In August, Sharp filed a similar lawsuit against Samsung in federal court in the U.S. state of Texas. Samsung said Thursday it was pursuing federal lawsuits in Texas and Delaware against Sharp.

The string of lawsuits between the two companies -- two of the world's biggest makers of LCD panels -- highlight the bruising competition to develop better technology for products like hot-selling flat screen TVs.

Samsung said its complaint calls on the Washington-based trade commission to launch an investigation and order that Sharp products that allegedly infringe on Samsung's patents -- including LCD TVs, monitors, notebook computers and mobile phones -- be kept out of the U.S. market.

"Samsung has and will continue to vigorously protect itself against the infringement and unauthorized use of its intellectual property," Samsung said.

Separately, Samsung also said it asked the Tokyo District Court on Wednesday to prohibit the manufacture and sale in Japan of Sharp LCD TVs it claims incorporate technology that allegedly violates two Japanese patents owned by Samsung.

"Sharp is prepared to take appropriate legal countermeasures once it studies the complaints," company official Akinori Shibuya said from Osaka, where Sharp is headquartered, referring to both the trade commission filing and Samsung's lawsuits.

South Korean and Japanese electronics manufacturers have battled over alleged patent infringements in recent years.

Matsushita Electric Industrial Co. in November 2004 went to court seeking to halt Japan sales of plasma screens made by LG Electronics Inc., claiming the South Korean company was infringing on its patents. They settled the dispute by signing a cross-licensing agreement in April 2005.

In March this year, South Korea's Hynix Semiconductor Inc. and Japan's Toshiba Corp. declared an end to their legal feud, signing agreements to share semiconductor patents and products.