US stock indices opened lower on Monday after President Donald Trump announced plans to double tariffs on steel and aluminum imports.

At the open, the Dow Jones Industrial Average fell 70.1 points, or 0.17%, to 42199.94. The S&P 500 fell 15.0 points, or 0.25%, to 5896.68​, while the Nasdaq Composite dropped 50.7 points, or 0.27%, to 19063.06.

On Friday, Trump announced that he would double US tariffs on imported steel and aluminum to 50% starting mid-week.

Adding to investors’ worries, China on Monday rejected Washington’s accusations that it violated a pact to de-escalate tariffs and vowed to push ahead with countermeasures to safeguard its interests if necessary.