It comes against the backdrop of a war of words between Mr Trump and Mr Zelenskyy, after officials from the US and Russia met in Saudi Arabia for talks to end the war - without representatives from Kyiv or Europe present.
After Mr Zelenskyy complained of being excluded from the discussions, Mr Trump suggested the conflict could have been "settled very easily" and said "you [Ukraine] should have never started it".
Conservative leader Kemi Badenoch, who had been under pressure to condemn Mr Trump's attacks, earlier said Mr Zelenskyy "is not a dictator.
Earlier on Wednesday, former prime minister Boris Johnson, who was in office when the war began, claimed Mr Trump's statements are "not intended to be historically accurate but to shock Europeans into action".
Mr Trump has since hit back, saying Mr Zelenskyy "better move fast or he is not going to have a country left" and branding him a "dictator".
