U.S. Commerce Secretary Wilbur Ross holds a news conference at the Department of Commerce in Washington, D.C., U.S. March 10, 2017. REUTERS/Eric Thayer

WASHINGTON (Reuters) - U.S. Commerce Secretary Wilbur Ross said on Thursday an investigation he launched will determine whether Chinese and other foreign-made steel is a threat to U.S. national security.

Ross briefed reporters at the White House shortly before President Donald Trump was to sign a directive asking for the probe to be conducted with all deliberate speed.

Ross said China has increased its steel exports to the United States despite promises to reduce them and that it now commands 26 percent of the U.S. market.