French persistence in pursuing a diplomatic outcome to the crisis surrounding Ukraine appeared to produce a chance of a summit between U.S. President Joe Biden and Kremlin leader Vladimir Putin on the proviso that Russia keeps its army out of its neighbour’s territory.

French President Emmanuel Macron’s resolve culminated in statements that such a summit could be formally announced later this week. Macron spoke twice on Sunday to Putin and, despite some differences in interpretation, both leaders said they believed diplomatic avenues were not exhausted in the crisis triggered by the deployment of more than 100,000 Russian troops on Ukraine’s border.

The proposed summit was announced in Washington and Paris hours after the United States issued a fresh warning that Russian forces were poised for an attack on Ukraine within days.

Ukraine’s defence minister said talk of an imminent incursion was “inappropriate” as Russia had formed no strike groups in suitable places along the border where Western intelligence estimates say anywhere up to 190,000 troops have been deployed.

But Russian troops remained engaged in joint military exercises with forces from Moscow’s ally Belarus, which were extended despite a pledge by both countries that they would end at the weekend. And tension remained high in eastern Ukraine’s Donbas region, punctuated by new explosions and increasing exchanges of fire between Ukrainian forces and proxies controlling large stretches of territory.

Russia has repeatedly denied any intention of making an incursion into Ukraine eight years after annexing the Crimean peninsula and fomenting the rebellion in Donbas. But Putin says Western countries must respond to his urgent calls to provide “security guarantees”, including an undertaking that NATO will expand no further and Ukraine can never join.

Blinken, Lavrov to pave the way for the summit

A statement issued by the Elysée palace in Paris said Macron had proposed the summit between Biden and Putin, and then with all parties, “to discuss security and strategic stability in Europe”. Biden and Putin “both accepted the principle of such a summit.”

The summit would be prepared by U.S. Secretary of State Antony Blinken and Russian Foreign Minister Sergei Lavrov at a meeting scheduled for Thursday, the statement said. Macron, it added, “will work with all stakeholders to prepare the content of these discussions.” It was not clear which other parties might later be invited to take part in the process.

White House Press Secretary Jen Psaki said Biden had accepted the principle of a meeting “if an invasion hasn’t happened.

“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.”

Psaki’s conditional statement reflected general scepticism among U.S. analysts that the summit would go ahead.

Officials quoted by the New York Times said the proposal was being considered without any formal plans for its format and timing.

CNN said staging a summit with Putin represented a “significant gamble” for Biden.

“Hawkish Republicans are sure to accuse him of appeasing the Russian strongman and of rewarding his aggression in holding Ukraine hostage,” CNN said in a commentary. “If a meeting with Putin fails and an invasion follows regardless, Biden will open himself up to charges of weakness.”

Macron spoke to Putin for just short of a combined total of three hours, with the second call taking place well after midnight Moscow time. And in the intervening period between the calls, the French president spoke to Biden for about 15 minutes.

A Kremlin statement after Macron’s first contact with Putin did expose significant differences in interpreting events in Ukraine.

Putin accused Ukrainian security forces of escalating tensions in Donbas and complained of supplies of weaponry sent to Ukraine from Western countries. Macron, according to an Elysée statement, said the separatists in eastern Ukraine were largely responsible for the tension.

And the Kremlin said Putin stood by his insistence on “the need for the United States and NATO to take Russian demands for security guarantees seriously and respond to them concretely and to the point”.

Reports from Donbas indicated a big upswing at the weekend of ceasefire violations. The Russian proxies who have run large swathes of territory since 2014 ordered a mobilisation late last week and a mass evacuation. Russian sources said more than 10,000 had already crossed the border into Russia and journalists who spoke to them reported that many were bewildered and unhappy about having to leave.

Macron takes the lead for Europe

Macron has assumed a prominent role in pursuing European negotiation separately from Washington – two weeks ago he visited both Putin and Ukrainian President Volodymyr Zelensky, stressing what he saw as the importance of the two “Minsk agreements” signed in 2014 and 2015 and aimed at ending the conflict eastern Ukraine. Those accords call for autonomy and elections in occupied areas to be restored to Ukrainian control, but many in Ukraine have come to view the agreements as unworkable.

Earlier in the day, Blinken had cited new intelligence and the extension of the Russian-Belarusian military manoeuvres in saying he believed an incursion would proceed very soon.

“… Everything we’re seeing suggests that this is dead serious, that we are on the brink of an invasion,” Blinken told the CBS programme Face the Nation. “We will do everything we can to try to prevent it before it happens.  But equally, we’re prepared, if he does follow through, to impose massive consequences, to defend – to provide for Ukraine’s ongoing defence, and to bolster NATO.”

Blinken repeated Biden’s contention that Putin “has made the decision, but until the tanks are actually rolling and the planes are flying, we will use every opportunity and every minute we have to see if diplomacy can still dissuade President Putin from carrying this forward.

Blinken said he was further persuaded by the increase in military incidents in Donbas which Western officials say could be exploited by Russia as a pretext to launch an incursion.

U.S. officials have cited new intelligence that reveals that 40 to 50 percent of the Russian forces surrounding Ukraine have moved out of staging and into combat formation and could launch a full-scale invasion within days.

Defence Secretary Lloyd Austin said Russia had continued to build up its forces, including in Belarus. “They are uncoiling and now poised to strike,” he said in Warsaw.

Ukrainian Defence Minister Olexiy Reznikov cast doubt on an imminent Russian attack.

“As matters stand now, no Russian Federation strike groups have yet been formed in any place where they are surrounding Ukraine,” Reznikov told Ukrainian 1+1 television.

“So in my view, it is inappropriate to say that tomorrow or the day after tomorrow, there will be an attack. But this does not mean that the risks are low. It does not mean there is no threat.”

Zelensky has chided the United States and other allied countries for repeatedly warning of impending attacks, sometimes citing a specific date.

In a fiery address to the Munich security conference at the weekend, Zelensky also urged Western countries to impose sanctions now rather than wait for his country to suffer the effects of an incursion. Zelensky also called on Western nations to learn from past mistakes and end the “appeasement” of Russia.

He also sought clarity on the prospects for Ukraine securing membership of NATO and the European Union and said Ukrainians were resolved to defend their country, with or without support.

The Ukrainian president came to power on a pledge to strike a deal with Putin to end the Donbas conflict, but now says only NATO membership can solve the country’s problems – and seeking membership of Western organisations is now entrenched in the Ukrainian constitution.

NATO pledged at a 2008 summit that Ukraine and ex-Soviet Georgia would one day be members of the Alliance, but prospects for either country to meet the requirements are remote for now. The Alliance rejects Russia’s call to formally keep Ukraine out, saying such a move is at odds with its “open door” policy and is tantamount to dictating the orientation of a neighbouring country.