US president Joe Biden has agreed “in principle” to a meeting with Vladimir Putin, provided Russia holds off on what American officials believe is an imminent assault on Ukraine.
It came as heavy shelling continued on Monday in a conflict in eastern Ukraine that it is feared will spark the Russian offensive.
White House press secretary Jen Psaki said the US administration has been clear that America is “committed to pursuing diplomacy until the moment an invasion begins”.
Ms Psaki said of the proposed meeting brokered by French president Emmanuel Macron: “We are always ready for diplomacy. We are also ready to impose swift and severe consequences should Russia instead choose war.
“And currently, Russia appears to be continuing preparations for a full-scale assault on Ukraine very soon.”
US secretary of state Antony Blinken and Russian foreign minister Sergei Lavrov are set to meet on Thursday in Europe, provided Russia does not invade Ukraine.
Kremlin spokesman Dmitry Peskov said that Mr Putin and Mr Biden could meet if they consider it necessary, but emphasised that “it’s premature to talk about specific plans for a summit”.
“The meeting is possible if the leaders consider it feasible,” he said in a conference call with reporters.
Russia has rescinded earlier pledges to pull tens of thousands of its troops back from Ukraine’s northern border, a move that US leaders claimed put Russia another step closer to a planned invasion.
This action extends what the Kremlin said were military exercises, originally set to end on Sunday, that brought an estimated 30,000 Russian forces to Belarus, Ukraine’s neighbour to the north.
They are among at least 150,000 Russian troops now deployed outside Ukraine’s borders, along with tanks, warplanes and artillery.
The continued deployment of the Russian forces in Belarus raised concern that Russia could send those troops into the Ukrainian capital, Kyiv, a city of about three million people less than a three-hour drive away.
A US official said that Mr Biden’s assertion that Mr Putin has made the decision to roll Russian forces into Ukraine was based on intelligence that Russian front-line commanders have been given orders to begin final preparations for an attack.
The United States and many European countries have claimed for weeks that Mr Putin has built up the forces he needs to invade Ukraine – a westward-looking democracy that has sought to move out of Russia’s orbit – and is now trying to create pretexts to invade.
Western nations have threatened massive sanctions if Mr Putin moves his forces into Ukraine.
US officials on Sunday defended their decision to hold off on their planned financial punishments of Russia ahead of any invasion, after Ukrainian president Volodymyr Zelensky called for the West to do more.
“If you pull the trigger on that deterrent, well then, it doesn’t exist anymore as a deterrent,” Pentagon spokesman John Kirby told Fox News.
Russia held nuclear drills on Saturday as well as the conventional exercises in Belarus, and has ongoing naval manoeuvres off the coast in the Black Sea.
The announcement that Russia was reversing its pledge to withdraw its forces from Belarus came after two days of sustained shelling along a contact line between Ukraine’s soldiers and Russian-allied separatists in eastern Ukraine.
The separatist authorities said on Monday that at least four civilians were killed by Ukrainian shelling over the past 24 hours and several others were injured. Ukraine’s military said two Ukrainian soldiers were killed over the weekend, and another serviceman was wounded on Monday.
Ukrainian military spokesman Pavlo Kovalchyuk said the Ukrainian positions were shelled 80 times on Sunday and eight times early Monday, noting that the separatists were “cynically firing from residential areas using civilians as shields”.
He insisted that Ukrainian forces were not returning fire.
Amid the heightened invasion fears, the Kremlin reacted angrily to a New York Times report that the US administration has sent a letter to the United Nations human rights chief claiming that Moscow has compiled a list of Ukrainians to be killed or sent to detention camps after the invasion.
Mr Peskov said the claim was a lie and no such list exists.
Moscow denies any plans to invade Ukraine, but wants Western guarantees that Nato will not allow Ukraine and other former Soviet countries to join as members.
It also urges the alliance to halt weapons deployments to Ukraine and roll back its forces from eastern Europe – demands flatly rejected by the West.
Meanwhile, US vice president Kamala Harris said at a security conference in Munich, Germany: “We’re talking about the potential for war in Europe.
“It’s been over 70 years, and through those 70 years … there has been peace and security.”
After a call with Mr Macron, Mr Putin blamed Ukraine – incorrectly, according to observers there – for the escalation of shelling along the contact line, as well as Nato for “pumping modern weapons and ammunition” into Ukraine.
Mr Macron also spoke separately to Mr Zelensky, to Prime Minister Boris Johnson and to Mr Biden.
In the eastern Ukraine regions of Lugansk and Donetsk, separatist leaders have ordered a full military mobilisation and sent more civilians to Russia, which has issued about 700,000 passports to residents of the rebel-held territories.
The European Union’s top diplomat, foreign policy chief Josep Borrell, welcomed the prospect of a Biden-Putin summit but said the 27-nation bloc has finalised its package of sanctions for use if Mr Putin orders an invasion.
“The work is done. We are ready,” said Mr Borrell.
He provided no details about who might be targeted.
Ukrainian foreign minister Dmytro Kuleba said on Monday that the EU has also agreed to send military officers to the country in an advisory role.
It is likely to take several months to set up.