Ukraine and Russia called for intensified diplomatic efforts Sunday to avert all-out war, each blaming the other for a sharp escalation in shelling on the front line separating Kyiv's forces from Moscow-backed separatists.

After separate calls with France's President Emmanuel Macron, both Russian leader Vladimir Putin and Ukraine's Volodymyr Zelensky pressed for more talks.

Washington is warning a Russian invasion of Ukraine is imminent, and Macron's office dubbed the calls "the last possible and necessary efforts to avoid a major conflict in Ukraine".

US Secretary of State Antony Blinken said Russia remained "on the brink" of invading Ukraine, but promised that President Joe Biden was ready to talk to Putin and that Washington would seek a diplomatic solution until Russian "tanks are actually rolling".

During his 105-minute discussion with Macron, Putin said "the cause of the escalation is 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 he added that the two leaders "believe it is important to intensify efforts to find solutions through diplomatic means".

Frontline Tension

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", adding that both countries' foreign ministers would meet "in the coming days".

Macron, Biden, German leader Olaf Scholz and other allied leaders were to hold calls later Sunday, the Elysee said.

Moscow has demanded that the NATO alliance permanently rule out Ukraine's bid for membership and the withdrawal of Western forces deployed in eastern Europe since the end of the Cold War.

Zelensky called for an immediate ceasefire and the resumption of talks under the Trilateral Contact Group of Russia, Ukraine and the Organization for Security and Cooperation in Europe (OSCE).

"We stand for intensifying the peace process," he tweeted, adding that he had informed Macron about "new provocative shelling" on the front line between Ukrainian forces and Russian-backed rebels.

Macron paid tribute to Zelensky's "sang froid" in his determination to prevent an escalation, said a statement from his office.

Following the call, the OSCE said it would hold an extraordinary meeting on Monday to seek ways to de-escalate the situation.

Screws Tighten

Earlier, fears of escalation mounted after Belarus announced that Russian forces would remain on its soil after Sunday's scheduled end to joint drills.

Moscow had previously said the 30,000 troops it has in Belarus were carrying out readiness drills with its ally, to be finished by Sunday, allowing the Russians to head back to their bases.

The Belarus defence ministry said Putin and Belarus leader Alexander Lukashenko had decided to "continue inspections", citing increased military activity on their shared borders and an alleged "escalation" in east Ukraine.

The French presidency nevertheless said Putin had once again told Macron that the Russian troops would eventually leave.

The extended drills will be seen as a further tightening of the screws on Ukraine, already facing increased shelling from Russian-backed separatist rebels and a force of what Western capitals says is more than 150,000 Russian personnel on its borders.

AFP reporters heard more bombardments overnight close to the front line between government forces and the Moscow-backed rebels who hold parts of the eastern districts of Lugansk and Donetsk.

In Zolote, a frontline village in the Lugansk region, an AFP reporter found residents hiding from the shelling in a shelter under a housing block, 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.

"This shelter, of course, is not equipped, but it saved people in 2014. There is no water here, people bring it with them."

Occupied Enclave

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 a Russian intervention.

"Russian military personnel and special services are planning to commit acts of terror in temporarily occupied Donetsk and Lugansk, killing civilians," claimed Ukraine's top general Valeriy Zaluzhniy.

"Our enemy wants to use this as an excuse to blame Ukraine and move in regular soldiers of the Russian armed forces, under the guise of 'peacekeepers'," he added.

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

"My husband told me: take the children and go!" 31-year-old nurse Anna Tikhonova told AFP from a camp at Vesselo-Voznessenka, Russia. She and her children had fled from Gorlovka, Ukraine, to the sound of gunfire, she said.

The volatile front line between Ukraine's army and the Russian-backed separatists has seen a "dramatic increase" in ceasefire violations, OSCE monitors have said.

Hundreds of artillery and mortar attacks were reported in recent days, in a conflict that has rumbled on for eight years and claimed more than 14,000 lives.