Trump pledges to match EU and Canada's retaliatory tariffs

US President Donald Trump has pledged to impose more tariffs after his latest move to introduce import taxes on steel and aluminium entering the US prompted retaliation from the European Union (EU) and Canada.

Trump said that "of course" he would respond to the countermeasures, repeating his warning to reveal "reciprocal" tariffs next month on countries around the world.

"Whatever they charge us with, we're charging them," he said.

The threat marked a further escalation of a trade war which has rattled financial markets amid concerns over the impact on the economies and consumers in many countries around the world, including the US.