Italy's Giorgia Meloni, Canada's Justin Trudeau and Belgium's Alexander De Croo travelled with European Commission President Ursula von der Leyen to Kyiv this morning.
They arrived by overnight train from neighbouring Poland.
Their presence is aimed at underlining the West's continuing support for Ukraine even as growing shortages of military supplies affect its performance on the battlefield.
Ms Von der Leyen wrote on X that she was in Kyiv "to celebrate the extraordinary resistance of the Ukrainian people".
She added: "More than ever, we stand firmly by Ukraine. Financially, economically, militarily, morally. Until the country is finally free."
Ms Meloni and Mr Trudeau are expected to sign security pacts with Ukrainian President Volodymyr Zelenskyy during their brief stay, in line with deals recently agreed with France and Germany that are worth billions of dollars.
