GENEVA (AP) — The head of the World Trade Organization says his agency is “clearly concerned” about President Donald Trump’s plan to impose tariffs on imported steel and aluminum and is warning of the potential for escalation.

Roberto Azevedo says a “trade war is in no one’s interests.”

A WTO spokesman relayed Azevedo comments to The Associated Press in an email just hours after President Donald Trump tweeted: “When a country (USA) is losing many billions of dollars on trade with virtually every country it does business with, trade wars are good, and easy to win.”

Azevedo warned: “The potential for escalation is real, as we have seen from the initial responses of others.”

He said the WTO “will be watching the situation very closely.”