FILE PHOTO: U.S. Trade Representative Robert Lighthizer testifies before a Senate Finance Committee hearing on "President Trump's 2018 Trade Policy Agenda" on Capitol Hill in Washington, U.S., March 22, 2018. REUTERS/Kevin Lamarque/File Photo

WASHINGTON (Reuters) - The United States launched five separate World Trade Organization dispute actions on Monday challenging retaliatory tariffs imposed by China, the European Union, Canada, Mexico and Turkey following U.S. duties on steel and aluminum.

The retaliatory tariffs on up to a combined $28.5 billion worth of U.S. exports are illegal under WTO rules, U.S. Trade Representative Robert Lighthizer said in a statement.

“These tariffs appear to breach each WTO member’s commitments under the WTO Agreement,” he said. “The United States will take all necessary actions to protect our interests, and we urge our trading partners to work constructively with us on the problems created by massive and persistent excess capacity in the steel and aluminum sectors.”

Lighthizer’s office has maintained that the tariffs the United States has imposed on imports of steel and aluminum are acceptable under WTO rules because they were imposed on the grounds of a national security exception.

Mexico said it would defend its retaliatory measures, saying the imposition of U.S. tariffs was “unjustified.”

“The purchases the United States makes of steel and aluminum from Mexico do not represent a threat to the national security,” Mexico’s Economy Ministry said in a statement.

“On the contrary, the solid trade relationship between Mexico and the U.S. has created an integrated regional market where steel and aluminum products contribute to the competitiveness of the region in various strategic sectors, such as automotive, aerospace, electrical and electronic,” the ministry added.

Lighthizer said last month that retaliation had no legal basis because the EU and other trading partners were making false assertions that the U.S. steel and aluminum tariffs are illegal “safeguard” actions intended to protect U.S. producers.