The leaders of the United Kingdom, France, Germany, Poland and Ukraine set the start of the ceasefire for May 12 at a meeting in Kyiv, during which they held a phone call with Trump.
"So all of us here together with the US are calling Putin out. If he is serious about peace, then he has a chance to show it," UK Prime Minister Keir Starmer told a press conference.
"No more ifs and buts, no more conditions and delays."
Soon after the European leaders' announcement, the Kremlin appeared guarded.
"We hear many contradictory statements from Europe. They are generally confrontational in nature rather than aimed at trying to revive our relations. Nothing more," Kremlin spokesman Dmitry Peskov was quoted as saying by Russian news agency Interfax.
Putin "has repeatedly said that he is ready for contacts with any leaders," Peskov said.
"And he is open to interaction, to dialogue with any leaders to the extent that the leaders themselves are ready."
Sanctions against Russia have been toughened repeatedly since its full-scale invasion in 2022, without ending the war.
Trump, who did not immediately comment publicly on the European leaders' remarks, has also signalled frustration with what the US views as Putin's foot-dragging over a ceasefire.
"In the event that the ceasefire is violated, massive sanctions will be prepared, in co-ordination between the Europeans and the United States," French President Emmanuel Macron said.
By imposing new sanctions, the White House would be aligning itself more closely with western Europe, which has been rattled by a trade war in which Trump has imposed tariffs on them and other countries.
Ukrainian President Volodymyr Zelenskiy said he and the visiting leaders had agreed the unconditional ceasefire must start on Monday and cover air, sea and land.
If Russia refused, it would face new sanctions, including the strengthening of punitive measures targeting its energy and banking sectors, he said.
Peskov had been quoted as saying on Friday that Russia supported the implementation of a 30-day ceasefire but only with due consideration of "nuances".
In remarks to US broadcaster ABC, Peskov had suggested foreign military assistance for Ukraine must stop for a temporary ceasefire to take effect.
"Otherwise it will be an advantage for Ukraine," he said.
Macron said that if the ceasefire went ahead, it would be monitored mainly by the US while European countries would contribute.
The European leaders said the terms of a peace deal would be negotiated during the 30-day pause in fighting.
"We have no illusions that the ceasefire will be breached," Zelenskiy said.
On the eve of the summit, the US embassy in Kyiv warned of a "potentially significant" air attack in the coming days.
When the European leaders arrived in Kyiv by train on Saturday, a screen on the platform announced the arrival of the "Bravery Express".
Zelenskiy accompanied them as they paid their respects at a Kyiv memorial honouring Ukrainian soldiers killed in the war.
The visit falls on the final day of a May 8-10 ceasefire declared by Putin that Ukraine did not accept, denouncing it as a sham.
Both sides have accused each other of violating it.
Reuters journalists at a field hospital near the front line in Ukraine's Zaporizhzhia region saw soldiers being brought in with combat injuries sustained since the Russian ceasefire began.
"There hasn't been any ceasefire, shelling has continued just as before, drones are flying just like before, the same with explosives being dropped. Nothing has changed at all," said a wounded soldier who gave his name as Stanislav.
