President Donald Trump said Sunday he believes Ukrainian President Volodymyr Zelensky is prepared to concede Crimea to Russia as part of a peace deal, as negotiations to end the three-year war enter what U.S. officials called a critical phase.

Speaking to reporters in Bedminster, New Jersey, Trump stated, "Oh, I think so, yeah," when asked whether Zelensky might give up the Black Sea peninsula seized by Russia in 2014. Trump added that Crimea was "12 years ago" and criticized former Presidents Barack Obama and Joe Biden for allowing Russia to annex the territory "without a shot being fired."

Trump met Zelensky on Saturday at the Vatican during the funeral of Pope Francis, their first face-to-face meeting since a contentious encounter at the White House in February. Trump described Zelensky as "calmer" and said, "I think he understands the picture, and I think he wants to make a deal."

During remarks Sunday, Trump urged Russian President Vladimir Putin to halt attacks on Ukraine. "I want him to stop shooting, sit down, and sign a deal," Trump said. He noted that the parties were "close" to an agreement but warned that if progress stalls, the U.S. might withdraw from mediation efforts.

U.S. Secretary of State Marco Rubio emphasized the urgency of the moment, telling NBC's Meet the Press, "It needs to happen soon. We cannot continue to dedicate time and resources to this effort if it's not going to come to fruition."

Russia continued military strikes following the Vatican meeting. Ukrainian President Zelensky said on Telegram that Russia had launched nearly 70 attacks on Sunday alone. "The situation at the front and the real activity of the Russian army prove that there is currently insufficient pressure on Russia from the world to end this war," Zelensky said.

The Biden and Trump administrations have floated proposals that would recognize Russian control over Crimea and freeze the current front lines, in contrast to European and Ukrainian positions that defer territorial negotiations until after a ceasefire is reached. German Defense Minister Boris Pistorius criticized the U.S. approach, stating, "Ukraine should not agree to all the steps reportedly set out in the deal proposed by Trump."

Chuck Schumer, Senate Majority Leader, warned against the U.S. abandoning Ukraine. "To just abandon Ukraine, after all the sacrifice that they made, after so much loss of life... it would just be a moral tragedy," Schumer said on CNN's State of the Union.

Russian Foreign Minister Sergei Lavrov said in a CBS interview that Russia targets only military sites, though recent missile strikes have killed civilians. "The target attacked was not something absolutely civilian," Lavrov said.

Meanwhile, Russian and Ukrainian forces continued cross-border strikes. Ukraine reportedly launched a drone attack on Russia's Bryansk region Sunday, killing one civilian. Moscow claimed over the weekend to have reclaimed control of the Kursk region, where North Korean troops have reportedly deployed to assist Russian forces.