The proposed tariffs, which range from 25 to 50 percent, would not directly target Russia but would penalize foreign countries that continue trading with it.

With much fanfare, the U.S. on March 25 announced it had brokered an agreement between Russia and Ukraine to "eliminate the use of force" in the Black Sea after two days of talks in Saudi Arabia. But while Kyiv said it was ready to abide by it straight away,

Donald Trump has threatened Ukrainian President Volodymyr Zelensky with "big problems" should not sign a controversial mineral death with the US. "He's trying to back out of the rare earth deal," Mr Trump told reporters on Air Force One.

U.S. President Donald Trump has reeled in his criticism of Vladimir Putin, appearing to call the Russian leader trustworthy while threatening Ukrainian President Volodymyr Zelensky with "big, big problems" over delays to the planned mineral deal between Washington and Kyiv.