The European Union said it would respond with "firm and proportionate countermeasures" after U.S. President Donald Trump's decision to impose tariffs on all steel and aluminium imports, escalating fears of a trade war.

President Donald Trump signed an order Monday imposing global tariffs of 25% on all steel and aluminum imports in a move that will likely please domestic steelmakers but hurt allies like Canada and Mexico.

The European Union plans to safeguard its economic interests by imposing countermeasures in response to the U.S. tariffs, according to EU officials.