The US will be introducing stringent new tariffs on steel and aluminum imports later this month, after president Donald Trump signed a declaration that will bring them into effect.

During a White House ceremony, the Republican leader confirmed that a 25 per cent import duty will be imposed on steel imports, in addition to a ten per cent tariff on aluminum. Canada and Mexico will be exempt from these duties, reflecting their ongoing negotiations with the US over a reorganization of the North American Free Trade Agreement (NAFTA).

According to President Trump, the protectionist move is designed to benefit the domestic steel and aluminum industries, which he believes have been damaged by foreign imports. He said the tariffs align with his intentions to protect the US "from other countries coming in and stealing our wealth and stealing our jobs and stealing our companies".

US trade representative Robert Lighthizer added: "Under the leadership of President Trump, America has a robust trade agenda that supports our national security. The president is once again demonstrating he will protect our country, fight for American workers and strictly enforce our trade laws."

Internationally, the decision has been met with extreme concern, with global markets experiencing a significant dip in the wake of the announcement, as major trading partners now fear a full-scale trade war with the US.

China's steel and metals associations are already calling for retaliation, urging the government to target US imports including coal, agricultural products and electronics, while South Korea is threatening to take the issue before the World Trade Organization.

Other key partners - including the UK, EU and Australia - said they will be seeking to receive exemptions from the tariffs in line with those provided to Canada and Mexico, with both NAFTA partners also opposing the move despite their exclusion from it.