Ukraine and its allies on Monday sought to pile pressure on Russia to agree to an unconditional truce, with European leaders threatening to immediately impose a new round of sanctions and President Volodymyr Zelensky challenging President Vladimir V. Putin to meet him in Turkey on Thursday.
President Trump raised the stakes, suggesting he might take part in such a meeting — an idea quickly seized on by Mr. Zelensky, the Ukrainian leader, who has been trying to align himself with a U.S. leader who has at times seemed hostile to him.
“I supported Donald Trump with the idea of a complete and unconditional cease-fire,” Mr. Zelensky said in a statement on Monday night. “I supported President Trump with the idea of direct talks with Putin.”
He added: “Of course, all of us in Ukraine would like President Trump to be there with us — at this meeting in Turkey. This is the right idea.”
The Kremlin declined to comment on whether Mr. Putin would take Mr. Zelensky up on his challenge, issued on Sunday, to meet personally on Thursday, and did not immediately respond to the suggestion that Mr. Trump might attend a summit of the three leaders.
But Mr. Trump, speaking to reporters at the White House, picked up on Mr. Zelensky’s proposal, saying, “Don’t underestimate Thursday in Turkey.” He then suggested that he might alter his travel plans, which have him in the Middle East that day, and go to Turkey to take part in the meeting, depending on how the hoped-for talks go.
Secretary of State Marco Rubio has already announced plans to travel to Turkey this week to attend the informal NATO foreign ministers meeting scheduled there from Wednesday to Friday.
The statements from Kyiv and Washington were the latest turn in an increasingly frenetic round of diplomatic brinkmanship, as the Trump administration grows frustrated by a lack of progress in its efforts to end the bloodiest conflict in Europe in generations.
Earlier Monday, European leaders leaned on Moscow to accept, by the end of the day, an unconditional 30-day truce that was first proposed by the United States in early March and immediately accepted by Ukraine, or face another round of punishing sanctions.
“The clock is ticking — we still have 12 hours until the end of this day,” the German government spokesman, Stefan Kornelius, said at a news conference.
The Kremlin spokesman brushed off the threat. “The language of ultimatums is unacceptable — you cannot talk to Russia like this,” the spokesman, Dmitri S. Peskov, told Russian news agencies.
Mr. Putin has so far rejected the cease-fire proposal, and over the weekend, he called instead for renewed negotiations between Russia and Ukraine, though not by their leaders. Ukrainian officials, their European allies and even, recently, Mr. Trump, have questioned whether Mr. Putin really wants to end the war.
The offer to meet face to face was intended to make it clear that the “the ball is in Moscow’s court,” in effect calling Mr. Putin’s bluff, Andriy Yermak, Mr. Zelensky’s chief of staff, told the Ukrainian news outlet RBC-Ukraine. Kyiv, he said, is accustomed to the Kremlin’s stalling tactics.
“We won’t give Russia reason to accuse us of sabotaging the peace process,” Mr. Yermak said.
Ukraine, along with its European allies, continued to insist on Monday that the fighting needed to stop before serious negotiations could get underway.
President Emmanuel Macron of France said that Kyiv had shown itself willing time and again to make concessions in order to begin the hard work of brokering a lasting peace. “Either Russia — Mr. Putin — is serious and wants peace, or it’s not serious and we have to impose even more sanctions,” Mr. Macron told reporters.
Britain’s foreign secretary, David Lammy, told reporters in London that it was time for Russia to stop stalling. “This is the time for Vladimir Putin to get serious about peace in Europe, to get serious about a cease-fire, and to get serious about talks,” he said.
When the leaders of France, Germany, Britain and Poland traveled to Kyiv over the weekend to deliver that same message, they were careful to coordinate their efforts with the White House. They made clear that only agreeing to an unconditional cease-fire would spare Moscow additional sanctions targeting oil exports and banking — and said that the United States would also impose sanctions on Russia if Mr. Putin did not agree to a truce.
However, after Mr. Putin made a counteroffer of direct talks without mentioning a cease-fire, President Trump urged the Ukrainians to attend the meeting. “Ukraine should agree to this, IMMEDIATELY,” Mr. Trump wrote on Sunday in a statement on social media.
Mr. Zelensky responded swiftly, seemingly seeking to flip the script on the Russian leader by saying that he agreed to negotiations in any format and that he would travel to Turkey to meet with Mr. Putin — personally.
Nataliya Vasilyeva, Christopher F. Schuetze, Aurelien Breeden and Stephen Castle contributed reporting.
