WASHINGTON, April 24 (Reuters) - U.S. Commerce Secretary Wilbur Ross said on Monday his agency will impose new anti-subsidy duties averaging 20 percent on Canadian softwood lumber imports, a move that escalates long-running trade dispute between the two countries.

"There are several different layers of duty each for a different company, but it averages 20 percent," Ross told Reuters by telephone. "It affects $5 billion worth of lumber coming in from Canada. It's about 31.5 percent of the total U.S. market, so it's a pretty big deal in terms of the Canadian relationship." (Reporting by David Lawder; Editing by Sandra Maler)