Any attempt to get Ukraine into Nato will run into a “buzz saw” in Washington unless Europe pays for it, a top diplomat for Donald Trump has said.

Richard Grenell, a US special presidential envoy, suggested that US taxpayers would not be prepared to fund Ukrainian membership of the Western alliance.

However, he appeared to leave the door open to expansion in future if European countries were prepared to shoulder more of the financial burden for defending the Continent.

His comments came just minutes after Mark Rutte, Nato’s secretary general and the former prime minister of the Netherlands, warned that Russian president Vladimir Putin should not be allowed to “veto” Ukraine joining the military alliance.