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.

Volodymyr Zelensky issued an 11-word warning to Donald Trump as the spoke at Pope Francis' funeral on Saturday, a lip reader claims. In extraordinary footage, the two leaders sat face to face and reportedly had a 15-minute discussion in St Peter's Basilica shortly before the ceremony began as negotiations to end Russia's war in Ukraine continue.

The United States has been pushing Ukraine to accept a peace plan that seems in part a gift to Moscow. But the short meeting of the leaders, and subsequent comments, appeared to be a change in tone.