Three European prime ministers rode a train for Kyiv on Tuesday, the first visit by foreign leaders to the Ukrainian capital since Russia launched its invasion, and a striking symbol of Ukraine's success so far in fending off Russia's assault.

"It is our duty to be where history is forged. Because it's not about us, but about the future of our children who deserve to live in a world free from tyranny," said Polish Prime Minister Mateusz Morawiecki, who set off across the border with Czech Prime Minister Petr Fiala and Janez Jansa of Slovenia.

Fiala said the aim was...