LONDON, June 1 (Xinhua) -- British Prime Minister Theresa May on Friday said she was "deeply disappointed" at the unjustified decision by the United States to apply tariffs to European Union (EU) steel and aluminium imports.

Her comments came one day after the U.S. President Trump announced the decision to levy tariff amid waves of criticism.

May said in a statement that the United States, the EU and Britain 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 U.S. industry including in defence projects which bolster U.S. national security," she said.

"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," the prime minister added.

The tariffs of 25 percent on steel products and 10 percent on aluminium, which affect the EU, Canada and Mexico, came into effect on Friday.