The president appears to have adopted a proposal first made last year that offers “strategic partners” such as the U.S. special access to Ukraine's glut of natural resources.

It will be three years since Russian president Vladimir Putin ordered his army to invade neighbouring Ukraine on February 24. Mr Putin said Russia was intervening as an act of self-defence. Russia did not want to occupy Ukraine, he said, but would demilitarise and "de-Nazify" the country.

President Donald Trump said he wants Ukraine to give the US rare earth metals in exchange for aid in its war with Russia. Speaking to reporters at the White House on Monday, the president said he wanted to get guarantees on a supply of "very valuable rare earth" materials from Ukraine in return for US military equipment.