Local residents attend an all-Ukrainian training campaign "Don't panic! Get ready!" close to Kyiv, Ukraine.

The Kremlin warned Monday there are no concrete plans for a summit between the Russian and US leaders, as diplomats scrambled to head off the threat of a Russian invasion of Ukraine.

The idea of a meeting between presidents Vladimir Putin and Joe Biden has been championed by France and cautiously welcomed by Ukraine as a way to avert a catastrophic war in Europe.

But Putin's spokesman Dmitry Peskov said: "It's premature to talk about any specific plans for organising any kind of summits" adding that no "concrete plans" had been put in place.

France's President Emmanuel Macron called Putin on Sunday and afterwards his office said that both the Russian and Biden were open to the idea.

The summit would go ahead, however, only "on the condition that Russia does not invade Ukraine."

"There is a diplomatic hope," France's minister for European affairs Clement Beaune told LCI television.

"If there is still a chance to avoid war, to avoid a confrontation and build a political and diplomatic solution, then we need to take it," he said.

But in Washington, a senior US administration official told AFP: "Timing to be determined. Format to be determined. So it's all completely notional."

Visiting Brussels, Ukraine's foreign minister welcomed the French effort.

"We believe that every effort aimed a diplomatic solution is worth trying," Dmytro Kuleba said ahead of a meeting with EU counterparts.

"We hope that the two presidents will walk out from the room with an agreement about Russia withdrawing its forces from Ukraine," he said.

Defence Minister Oleksiy Reznikov said there was no sign of Russian forces withdrawing from the border, and that Moscow-backed rebels continue to shell Ukrainian positions.

"Since the beginning of this day, as of 09:00, 14 attacks have already been recorded , 13 of them from weapons prohibited by the Minsk agreements," he told reporters in Kyiv.

"One of our soldiers was wounded," he said.

Russia annexed the Ukrainian region of Crimea in 2014 and Moscow-backed separatists hold an enclave in the eastern distracts of Lugansk and Donetsk.

In recent weeks, according to US intelligence, Moscow has massed more than 150,000 troops and sailors around Ukraine's borders in Belarus, Russia, Crimea and the Black Sea.

Biden has said that US intelligence believes that Putin has made a decision to invade Ukraine and that commanders are readying units to attack within days.

Russia has long denied this, but state media accuse Kyiv of preparing a murderous assault against the rebel enclave, and has started evacuating civilians from the area.

Kyiv and Washington accuse the Russians of plotting a "false flag" operation to fake Ukrainian atrocities in order to serve as a pretext for an all out assault.

Meanwhile, Ukraine and Russia continue to blame each other for a spike in shellings on the front line separating Kyiv's forces from Moscow-backed separatists.

The bombardments have sent Ukrainians fleeing to cellars and other shelters, while some civilians have been evacuated.

The idea for a summit came moments after Macron held his second marathon call with Putin of the day.

During their first, 105-minute discussion, Putin blamed the increase in violence on the front line on "provocations carried out by the Ukrainian security forces", according to a Kremlin statement.

Putin repeated a call for "the United States and NATO to take Russian demands for security guarantees seriously".

But Macron's office also said the two had agreed on "the need to favour a diplomatic solution to the ongoing crisis and to do everything to achieve one".

The second time the pair spoke, late Sunday evening, it was for an hour, the French presidency said. The announcement of the summit came shortly after.

- 'Shelling again' - In Zolote, a frontline village in the Lugansk region, an AFP reporter found residents hiding in an earth-floored cellar roughly furnished when the separatist conflict erupted in 2014.

"These weeks they started shelling harder. Now they are shelling again," said 33-year-old handyman Oleksiy Kovalenko.

In Moscow, the US embassy warned Americans of potential attacks in public places in Russia.

Fears of escalation mounted Sunday when Belarus said Russian forces would remain on its soil after Sunday's scheduled end to joint drills, within striking distance of Ukraine.

The Moscow-backed separatists have accused Ukraine of planning an offensive into their enclave, despite the huge Russian military build-up on the frontier. Kyiv and Western capitals ridicule this idea, and accuse Moscow of attempting to provoke Ukraine and of plotting to fabricate incidents to provide a pretext for Russian intervention.

The rebel regions have made similar claims about Ukraine's forces and ordered a general mobilisation, evacuating civilians into neighbouring Russian territory.