Ukraine's President Volodymyr Zelensky had a 30 minute meeting with US Vice President JD Vance and Secretary of State Marco Rubio on the sidelines of Pope Leo XIV's inauguration.
It was the first meeting between Mr Zelensky and Mr Vance since they clashed during talks at the White House in February over the future of the war in Ukraine.
A Ukrainian official said they discussed the upcoming phone call planned between US President Donald Trump and Russian President Vladimir Putin.
Earlier, Pope Leo XIV held his first private audience as Catholic leader with Mr Zelensky, after highlighting the hopes for peace for a "martyred Ukraine".
"The martyred Ukraine is waiting for negotiations for a just and lasting peace to finally happen," the 69-year-old pope said in a prayer after the mass.
Mr Zelensky lined up to shake hands with Pope Leo afterwards, and then he and his wife joined the pontiff for a private audience.
Watch: Volodymyr Zelensky meets US Vice President JD Vance in Rome
In a video published by the Vatican, the Pope told the Ukrainian leader: "Nice to see you again."
When they were all seated, he apologised for making the couple wait.
As is customary, they also exchanged gifts.
Pope Leo only had two private audiences today.
The other was with President Dina Boluarte of Peru, a country where the pontiff worked as a missionary for two decades and of which he also has citizenship.
Earlier, in his homily, Pope Leo said he wanted the Church to be a "leaven for a reconciled world", calling for peace.
In response, Mr Zelensky wrote on Telegram: "We are grateful for the special words spoken today at the solemn mass about the need for a just peace and for the attention given to Ukraine and our people.
"Every nation deserves to live in peace and security."
He offered his congratulations to the Pope "on the beginning of such a special mission".
"May the prayers for a just peace and a dignified life for all people be heard," he said.
The late Pope Francis met Mr Zelensky several times and repeatedly called for peace in Ukraine, even appointing a special envoy who visited Kyiv and Moscow.
But many Ukrainians remember him bitterly for failing to clearly blame Russia for its invasion and calling for Ukraine to raise the "white flag".
Russia and Ukraine held their first direct talks in more than three years this week but did not agree a truce.
In his Regina Coeli prayer at the end of the mass, Leo also noted: "In Gaza, children, families and elderly survivors are reduced to hunger."And he recalled how "in Myanmar, new hostilities have destroyed innocent young lives".
