Washington DC - Vice President JD Vance rejected suggestions Moscow is slow-walking a potential peace deal in Ukraine, saying Russia has made "significant concessions" to Donald Trump over its demands for ending the war.

In a pre-recorded interview that aired Sunday, Vance insisted Trump, who met his Russian presidential counterpart Vladimir Putin this month at an Alaska summit, has been engaged in "very aggressive, very energetic diplomacy" with both Moscow and Kyiv in a bid to find a compromise solution that would stop the killing.

Trump has been championing a bilateral meeting between the Ukrainian and Russian presidents, but both sides have blamed each other for not wanting the talks to come through.

And as Russian Foreign Minister Sergei Lavrov accused Western countries on Sunday of trying to "block" peace negotiations, Vance offered a more conciliatory approach to Washington's longtime adversary, saying Russia was not stringing Trump along.

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"I think the Russians have made significant concessions to President Trump for the first time in three and a half years of this conflict," Vance told NBC talk show Meet the Press with Kristen Welker.

"They've actually been willing to be flexible on some of their core demands."

Vance said Moscow has conceded "the recognition that Ukraine will have territorial integrity after the war" – although he notably did not address whether a post-war Ukraine would have the boundaries it did before Moscow's invasion.

He also stressed that Russia has "recognized that they're not going to be able to install a puppet regime in Kyiv."

"Again, have they made every concession? Of course, they haven't," he added, "But we're making progress."

Vance said Washington would continue playing an active role in ensuring Ukraine has its security guarantees, but insisted "the president's been very clear: there are not going to be boots on the ground in Ukraine."

On the same Meet the Press program, one of Trump's key Democratic critics, Senator Adam Schiff of California, described the Trump-Putin summit as a failure that allowed the Russian leader to walk away with no ceasefire and a diminished threat of sanctions.

"So they strung him along successfully," Schiff said, adding he believes that peace talks have "stalled."

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The Democrat also slammed Russia's recent bombing of a US-owned factory in Ukraine as a provocative, "in-your-face" action against Trump, who has expressed little outrage about the incident other than to say he is "not happy."

Lavrov, speaking on the same show, briefly addressed the attack, and said he believes some critics are "really naive" to think such a factory was not involved in Ukraine's military effort.