Ukrainian Foreign Minister Andrii Sybiha‎ has accused Vladimir Putin of "wasting the world's time", a day after high-stakes talks between the US and Russia over ending the war in Ukraine failed to produce tangible results.

"Russia must end the bloodshed it has started. If this doesn't happen and Putin just spits into the world's face once again, there must be consequences," Sybiha said.

Still, Sybiha added that the US delegation had told his colleagues that the talks had been of "positive significance for the peace process" and they had invited Ukrainian officials to continue talks in the US in the near future.

President Donald Trump's special envoy Steve Witkoff and his son-in-law Jared Kushner spent almost five hours with Putin at the Kremlin on Tuesday and the White House said on Wednesday they had briefed Trump after a "thorough, productive meeting".

The US-Russia talks followed days of US meetings with Ukrainian and European leaders, after concerns had been expressed that a deal was being hatched that was too slanted towards Russia's demands.

Putin's senior policy adviser Yuri Ushakov said "no compromise" on ending the war had been found. "Some of the US proposals look more or less acceptable, though they need to be discussed further", he said, while adding that others had been openly criticised by Russia's leader.

Although Ushakov did not elaborate further, at least two major points of contention remain between Moscow and Kyiv - the fate of Ukrainian territory seized by Russian forces and security guarantees for Ukraine.

Kyiv and its European partners believe that, even in the event of a peace deal, the most effective way to deter Russia from attacking again in the future would be to grant Ukraine membership of Nato.

Russia is vehemently opposed to such a proposal, and Trump too has repeatedly signalled he has no intention of letting Kyiv into the alliance.

The prospect of Ukraine joining Nato was a "key question" that was tackled in Moscow, the Kremlin said on Wednesday.

Ushakov implied that the Russian negotiating position had been strengthened thanks to recent successes on the battlefield.

Russian soldiers had "helped make the assessments of our foreign partners regarding the paths to a peace settlement more appropriate," he said.

Ahead of the US visit to the Kremlin, Putin was filmed in army fatigues at a Russian command post, being briefed by commanders claiming the conquest of the key strategic city of Pokrovsk, in eastern Ukraine, as well as other nearby settlements.

Fighting in Pokrovsk is continuing and Russian forces do not control the whole city, but Russian officials clearly believe their message of military gains has been heard by the US.

Russian forces have made some incremental advances in the east and appear to have stepped up their campaign in recent weeks. They seized about 701 sq km (270 sq miles) of Ukrainian territory in November, according to AFP analysis of data from the US-based Institute for the Study of War (ISW), and they now control 19.3% of Ukrainian territory.

The Kremlin on Wednesday said Putin was ready to keep meeting with the Americans "as many times as needed".

But as Russian-American relations appear to grow more cordial, the gulf between Moscow and Europe widens.

Putin has accused Europe of sabotaging Russia's relations with the US, of putting forward demands Moscow could not accept and of blocking the peace process. Shortly before meeting Witkoff and Kushner, Putin told a forum in Moscow that while he did not want conflict with Europe, he was "ready for war".

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