Russia will make no major concessions on a peace plan for Ukraine, a senior Russian diplomat said on Wednesday, while a top Ukrainian official stressed that Kyiv will not amend its Constitution as part of any potential peace deal.

The latest peace proposal surprised officials in Washington, Europe and Kyiv, raising concerns that President Donald Trump may pressure Ukraine to sign a peace deal highly favorable to Moscow.

The plan prompted unusually sharp pushback from Trump's fellow Republicans, who have largely supported him since the start of his second term.

Senator Mitch McConnell, the party's former Senate leader, said Russia should not be rewarded. "A deal that rewards aggression wouldn't be worth the paper it's written on. America isn't a neutral arbiter, and we shouldn't act like one," he said on X.

Trump later insisted that progress was being made and Moscow was offering concessions.

Too early to talk of peace, Kremlin says

While welcoming the Trump administration's efforts, Russian Deputy Foreign Minister Sergei Ryabkov told reporters in Moscow on Wednesday: "There can be no question of any concessions, or any surrender of our approaches to those key points."

Trump said on Tuesday U.S. envoy Steve Witkoff  would meet Putin and that Jared Kushner – who helped negotiate the deal that brought about an uneasy Gaza ceasefire – would also take part.

"As for Witkoff, I can say that a preliminary agreement has been reached that he will come to Moscow next week," Russian presidential aide Yuri Ushakov told reporters.

Asked whether a peace deal was close, Kremlin spokesperson Dmitry Peskov said it was “premature” to make such an assessment, according to Russian News Agency Interfax.

Ukraine disagrees about constitutional amendments in peace deal

Ukraine will not amend its Constitution as part of any potential peace deal, Interfax-Ukraine reported on Wednesday, citing Oleksandr Bevz, an adviser to the head of Ukraine's presidential office and a member of the Ukrainian delegation involved in talks with the United States, partners and Russia.

"We have stated that Ukraine will not accept any form of recognition, and Ukraine will not make any changes to the Constitution – these are red lines," said Bevz.

He said territorial issues should be addressed on two principles: the current contact line should serve as the basis for talks, and such questions must be handled at the level of national leaders.

According to head of the presidential office Andriy Yermak, Ukrainian and U.S. negotiators have reached agreement in principle on most elements of Washington's proposed peace plan, though it has been significantly revised from the original 28 points.

(With input from agencies)