South Korea's Industry Ministry said on Monday it will respond to the looming 50% U.S. tariff on steel products as part of its trade discussions with Washington in order to minimise the impact on industry.

Iron ore fell to its lowest level since early May alongside equity markets after President Donald Trump said he would double tariffs on steel and aluminum to help protect American workers.

The so-called TACO trade will be tested as markets wait to see if Trump will actually follow through with his latest threat or if he will put it on hold soon.

President Trump would invoke other tariff authorities if his appeal of a trade court's ruling isn't successful, Commerce Secretary Lutnick said.

The president's plan - where countries face between 11% to more than 100% tariffs on goods brought into the US - was announced in April. But the majority of the tariffs were paused by Trump for 90 days in the wake of stock market volatility.

President Trump is launching a new trade war, this time targeting steel, raising the tariffs from 25 percent to 50 percent. CNBC Senior Analyst, Ron Insana and James Sample, a law professor at Hofstra University,

Mr. Trump celebrated what he calls a partnership between U.S. Steel and Japan-based Nippon on Friday, sharing details about commitments in the partnership and increased tariffs on imported steel.