French President Emmanuel Macron, German Chancellor Olaf Scholz and Italian Prime Minister Mario Draghi have arrived in Kyiv, Macron's office said on Thursday.
BFM TV and other media on board the train showed footage of the three leaders sitting at the same table on the train. The train was due to arrive shortly in the Ukrainian capital, BFM said.
The visit has taken weeks to organize with the three men looking to overcome criticism within Ukraine over their response to the war.
The trip comes a day before the European Commission is due to make a recommendation on Ukraine's status as an EU candidate, something the biggest European nations have been lukewarm about.
Speaking in Romania on Wednesday, Macron said it was time for Europe to reassure Ukraine over its EU ambitions.
"We are at a point when we need to send clear political signals, us Europeans, towards Ukraine and its people when it is resisting heroically," he said, without giving details.
Kyiv has criticized France, Germany and, to a lesser extent, Italy, for alleged foot-dragging in their support for Ukraine, accusing them of being slow to deliver weapons and of putting their own prosperity ahead of Ukraine's freedom and security.
Oleksiy Arestovych, an adviser to Ukrainian President Volodymyr Zelensky, told German newspaper Bild this week he was concerned the three leaders would put pressure on Kyiv to accept a peace deal favorable to Russian President Vladimir Putin.
"They will say that we need to end the war that is causing food problems and economic problems ... that we need to save Mr. Putin's face," he said, referring to comments by Macron this month that it was vital not to humiliate the Russian leader.
Addressing this concern, Draghi said on Tuesday it was important for peace talks to open as soon as possible, but added they had to be "on terms that Ukraine deems acceptable."
Zelensky is expected to push his visitors to send more arms to help his hard-pressed army withstand the Russian invaders.
Ukraine has been particularly critical of Germany's military aid and the country's ambassador to Berlin, Andrij Melnyk, told German broadcaster NTV he expected Scholz to hand over heavy weapons that had been long-promised but not yet delivered.
Scholz has dismissed allegations he has held back much-needed military support, saying it was one of the biggest military and financial backers of Ukraine, and that it was taking time to train Ukrainian soldiers to use the sophisticated artillery systems that it was offering.