TOKYO (Reuters) - General Electric Co <GE.N> said on Friday it filed a complaint with the U.S. International Trade Commission against Mitsubishi Heavy Industries Ltd <7011.T> last month to halt U.S. imports of the Japanese firm's wind turbines.

GE said Mitsubishi Heavy's wind turbines infringed its patent on variable speed control technology, which helps maximize energy capture from wind.

A spokesman for Mitsubishi Heavy said: "We believe that there are no patent infringements as GE insists. It's very regrettable that GE suddenly filed a complaint."

The Japanese firm will respond once it receives a formal notice from the ITC, he added.

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Demand for renewable energy has been growing amid concerns about the environment and soaring oil prices.

Shares of Mitsubishi Heavy tumbled 5.4 percent to 440 yen on Friday, against a 3.3 percent drop in the benchmark Nikkei

<.N225>.

GE, a major wind turbine maker which competes with Denmark's Vestas Wind Systems A/S <VWS.CO> and Germany's Siemens AG <SIEGn.DE> in the wind business, has forecast $6 billion in 2008 wind power-related revenue, up from about $4 billion last year.

The company said on Thursday it had landed a $1 billion contract to supply electricity-generating wind turbines to Invenergy Wind LLC, its second billion-dollar contract with that company this year.

Mitsubishi Heavy, Japan's biggest wind power turbine maker, won an order last May worth about $1.3 billion for 788 wind turbines from five U.S. power companies.

(Reporting by Yoko Kubota; Editing by Hugh Lawson)