Ukraine and its European allies have been buoyed by Donald Trump's promise of security guarantees for Kyiv to help end the Ukraine war but face many unanswered questions, including how willing Russia will be to play ball, Reuters reported.

Ukrainian President Volodymyr Zelenskiy hailed Monday's extraordinary summit at the White House with Trump as a "major step forward" towards ending Europe's deadliest conflict in 80 years and towards setting up a trilateral meeting with Russia's Vladimir Putin and the U.S. president in the coming weeks.

Flanked by the leaders of allies including Germany, France and Britain at the summit, Zelenskiy's warm rapport with Trump contrasted sharply with their disastrous meeting at the Oval Office in February.

But beyond the optics, the path to a lasting peace remains deeply uncertain and Zelenskiy may be forced to make painful compromises to end a war that analysts say has killed or wounded more than 1 million people, according to Reuters.