President Donald Trump has expressed doubts that Russian President Vladimir Putin wants to end its war with Ukraine which has raged for more than three years.

US President Donald Trump and Ukrainian President Volodymyr Zelensky held crunch war talks in the heart of the Vatican minutes before the start of the funeral of Pope Francis on Saturday, as the White House mounts an increasingly urgent push to strike a peace deal in Ukraine.

Donald Trump has said he thinks Vladimir Putin might be taking him for a ride when it comes to ending the Ukraine war, which is into its third year. The questioning coincided with images surfacing of Trump engaging with Ukrainian President Volodymyr Zelensky and other key figures while at Pope Francis' funeral mass in St Peter's Square.