Secretary of State Marco Rubio accused Ukrainian President Volodymyr Zelenskyy of lying over US demands on Friday and voiced an openness to divert weapons earmarked for Kyiv to support the war on Iran.
Zelenskyy had said in an interview that the United States was pressing Ukraine to cede the eastern Donbas region to Russia before finalising any post-war security guarantees.
"That's a lie," Rubio told reporters when asked about Zelenskyy's remarks.
"I saw him say that and it's unfortunate he would say that, because he knows that's not true," Rubio said in Paris after talks with the Group of Seven industrialised nations.
"What he was told is the obvious: security guarantees are not going to kick in until there's an end to a war, because otherwise you're getting yourself involved in the war," Rubio said.
"That was not attached to, unless he gives up territory," Rubio said. "I don't know why he says these things. It's not true."
The attack on Zelenskyy was especially striking coming from Rubio, a former hawkish senator who has largely been seen as more supportive of the Ukrainian cause than some others in President Donald Trump's circle.
In a scene that went viral in February last year, Rubio sat sullenly in the Oval Office as Trump and Vice President JD Vance berated Zelenskyy, saying he was ungrateful for US assistance.
Recently, Trump has again criticised Zelenskyy, saying that he needs to accept compromises and comparing him unfavourably with Russian President Vladimir Putin.
Rubio said that the United States was open to shifting assistance to Ukraine after the United States and Israel attacked Iran.
"Nothing yet has been diverted, but it could," Rubio said.
"If we need something for America and it's American, we're going to keep it for America first."
But he said there had not yet been any change to the so-called Prioritised Ukraine Requirements List (PURL), a NATO initiative established after Trump's return in which European allies fund weapons requested by Ukraine that are purchased from the United States.
