Sir Keir Starmer has said the United States "is right" about the UK and Europe needing to take more responsibility for defence and security.
The prime minister reiterated the UK will "play our role" if required in Ukraine following a peace agreement after he earlier this week said the UK would send troops to be part of a peacekeeping force.
Mr Trump also said Sir Keir and French President Emmanuel Macron, who will visit the White House too this week, "haven't done anything" to end the war.
Donald Trump sparked an emergency meeting of European leaders this week after he said European NATO members should spend more on defence, while the US should spend less.
Sir Keir has promised Mr Zelenskyy he will make the case for safeguarding Ukraine's sovereignty when he meets with Mr Trump, who has called the Ukrainian president a dictator.
