UK Prime Minister Theresa May today tore into Donald Trump's 'unjustified' decision to slap hefty tariffs on steel amid fears the move will spark a global trade war, Daily Mail reported.

The PM urged the US President to exempt America's 'close allies' Britain and the EU from the 25 per cent levies.

And she vowed to work with other EU countries to 'protect and safeguard our workers and industries' threatened by the policy.

Mrs May said: "I am deeply disappointed at the unjustified decision by the US to apply tariffs to EU steel and aluminium imports.

"The US, EU and UK are close allies and have always promoted values of open and fair trade across the world.

"Our steel and aluminium industries are hugely important to the UK, but they also contribute to US industry including in defence projects which bolster US national security.

"The EU and UK should be permanently exempted from tariffs and we will continue to work together to protect and safeguard our workers and industries."