Trump has also threatened to introduce tariffs - a tax on imports - on goods from Canada and Mexico, but paused these for 30 days after both countries agreed to boost border security. The US president has said tariffs are needed to help the American economy and to "protect" the country from the "major threat of illegal aliens and deadly drugs".

Donald Trump is the first president to use the International Emergency Economic Powers Act to impose tariffs, teeing up likely legal battles that will test his executive authority.