Former U.S. President Donald Trump and Ukrainian President Volodymyr Zelenskyy are once again in disagreement over how to end the war in Ukraine. On Wednesday, Trump criticized Zelenskyy for refusing to accept Russia’s control over Crimea, a region Russia took from Ukraine in 2014.

U.S. Vice President JD Vance supported Trump’s position, saying that it might be time for Russia and Ukraine to accept a U.S. peace plan—or for the U.S. to step away. The plan would freeze the battle lines close to where they are now and focus on reaching a long-term peace.

Vance, while speaking in India, said, “The only way to stop the killing is for both sides to stop fighting and freeze the conflict.”

Since becoming president in January, Trump has pushed Ukraine to agree to a ceasefire and has eased pressure on Russia. He believes peace can be reached quickly, even saying during his campaign that he could end the war in just 24 hours if re-elected.

But Zelenskyy made it clear again on Tuesday that Ukraine will not give up Crimea. “There’s nothing to discuss. This goes against our constitution,” he said.

Trump responded on social media, calling that statement “inflammatory” and saying it makes peace harder to reach. He also said that Crimea was lost years ago and should not be part of the peace talks anymore.

Even though recent talks in London were emotional, Zelenskyy expressed hope for future progress. He said Ukraine will always follow its laws and believes the U.S. and other partners will support Ukraine’s decisions.

To back his point, Zelenskyy shared a statement from 2018 made by Mike Pompeo, Trump’s former Secretary of State, which said the U.S. does not accept Russia’s takeover of Crimea.

Trump later posted that the U.S. is close to making a peace deal and repeated his belief that once both leaders agree, the fighting will stop. He said the talks in London were “pretty good,” and added, “We just need two strong and smart people to agree.”