French President Emmanuel Macron claimed a breakthrough on Tuesday in his quest to defuse the Ukraine crisis, saying he had won assurances from Russia not to escalate matters.
Mr Macron said his trip to Moscow had succeeded in its aim of “freezing the game” to allow for Nato and the Kremlin to discuss their future.
“This objective for me is fulfilled,” he said after travelling to Kiev on Tuesday for talks with Ukrainian leaders. “I obtained that there will be neither a worsening nor an escalation.”
Mr Macron did not elaborate on what assurances he had received, and Moscow declined to corroborate his claims.
Russian President Vladimir Putin again warned that Ukraine’s potential membership of Nato could start conflict.
“The potential of the united organisation of Nato is not comparable to Russia’s one," Mr Putin said. "We understand this.
"But we also understand that Russia is one of the leading nuclear powers. It is even ahead of many on some modern components."
Kremlin spokesman Dmitry Peskov said the five-hour talks between Mr Macron and Mr Putin had produced “rational elements on the basis of which work can continue”.
Ukraine's President Volodymyr Zelenskiy also took a cautious tone, saying he was waiting for Russia to match any talk of de-escalation with action.
"I do not really trust words. I believe that every politician can be transparent by taking concrete steps," Mr Zelenskiy said.
Mr Macron’s trip is the centrepiece of a week of frantic diplomacy as European leaders and foreign ministers try to prevent war in Ukraine.
German Chancellor Olaf Scholz met Mr Macron and Polish President Andrzej Duda in Berlin on Tuesday evening for talks in a group of three known as the Weimar Triangle.
"We are united by the goal of maintaining peace in Europe through diplomacy and clear messages and the shared will to act in unison," Mr Scholz said.
Annalena Baerbock, Germany's Foreign Minister, was on the frontline of Ukraine's conflict with pro-Russian separatists, where she said the crisis could only be solved with diplomacy.
"We will not be able to solve this aggression from the Russian side militarily," she said, after Germany was criticised in some quarters for refusing to export weapons to Ukraine.
It follows a trip by Mr Scholz to Washington in which he sought to reassure allies that Germany was on the same page as the US and Nato.
US President Joe Biden said Mr Scholz had "the complete trust of the United States" and described Germany as "completely, totally, thoroughly reliable".
While trumpeting the success of his Russian trip, Mr Macron said it would take weeks or months before any concrete progress was made.
Russia continues to press for guarantees that former Soviet countries such as Ukraine and Georgia will not be admitted to Nato.
The alliance rejects this and says Moscow should tone down its aggressive posture if it wants fewer western troops in its orbit.
Ann Linde, the Foreign Minister of non-aligned Sweden, said on Tuesday that there could be no return to a Cold War situation where countries such as Ukraine are "relegated to satellite status" rather than being free to choose their own alliances.
But Ms Linde told an event at the London School of Economics that Sweden had no plans to join Nato at the moment.
Meanwhile, UK Prime Minister Boris Johnson told Russia that any invasion of Ukraine would backfire because it would only make Nato stronger.
After meeting Lithuanian Prime Minister Ingrida Simonyte, Mr Johnson said the UK stood by Nato and eastern European allies.
"We're shoulder to shoulder with you and all our Nato allies and we want to make clear that we support you," he said.
"We support you when it comes to the immigration issues in Belarus and all the questions that we're now facing."
The talks are taking place against the backdrop of military drills under way in Russia and about to start on the territory of its ally, Belarus.
On Tuesday, Russia's Defence Ministry said six large landing ships were moving from the Mediterranean to the Black Sea, where they will take part in the exercises.
Mr Putin’s remarks on his summit with Mr Macron praised France’s diplomatic efforts and indicated that he was ready to continue negotiations.
But he also criticised Nato after it insisted that Ukraine, Georgia and other countries near Russia could join the alliance if they chose to.
Mr Putin described the military build-up near Ukraine as troop movements on Russian territory that should be of no concern to Nato.
“Nato and its member states believe that they have a right to teach us where and how we can deploy our armed forces,” he said.