French President Emmanuel Macron, German Chancellor Olaf Scholz and Italian Prime Minister Mario Draghi arrived in Kyiv on Thursday for their first visit to Ukraine since the Russian invasion.
The leaders arrived on a special train from Poland, with images showing them descending onto a platform in the Ukrainian capital.
It is their first trip to Ukraine since the Russian invasion of the country launched on February 24.
Macron said they will meet President Volodymyr Zelensky and go to "a war site where massacres have been committed."
The French leader has called alleged Russian atrocities in towns near Kyiv "war crimes".
"This is a message of European unity addressed to Ukrainian men and women, of support," Macron said as he descended from the train.
He said he came "to talk about both the present and the future since the coming weeks, we know, will be very difficult."
The visit comes as Ukraine is pushing to be given official candidate status to join the European Union.
The trio had travelled onboard a special train that left Poland in the early hours of Thursday.
German media said they had met "in the night" in Poland's south-eastern city of Rzeszow, which has an international airport.
They arrived separately and met on board shortly after the train's departure.
The French leader had just finished a visit to Moldova, one of Ukraine's neighbours.
Romanian leader Klaus Iohannis is due to join his French, German and Italian counterparts in Kyiv later on Thursday.
Other Western leaders have also visited Kyiv in recent weeks, after the Russian army retreated from its advance on the Ukrainian capital at the start of the invasion.