The Organization for Security and Co-operation (OSCE) in Europe will hold an extraordinary meeting of permanent representatives on Monday to find ways to de-escalate the situation in Ukraine, the Polish chairmanship of the European security body has said.
"The meeting has been called for Monday," Deputy Foreign Minister Pawel Jablonski said, following a request from Kyiv amid a sharp escalation in the conflict in eastern Ukraine.
OSCE monitors have reported hundreds of artillery and mortar attacks in recent days, in a conflict that has rumbled since 2014 and claimed more than 14,000 lives.
The ceasefire violations come as the United States accuses Russia of planning to invade Ukraine, after a build-up of some 150,000 troops on its ex-Soviet neighbour's borders.
Russia has denied any such plans.
Ukraine had requested a meeting of the OSCE Permanent Council in Vienna to discuss the "rapidly deteriorating security situation", Poland's OSCE representative Adam Halacinski said on Twitter.
It comes as both Ukraine and Russia called for intensified diplomatic efforts to avert all-out war, but blamed each other for a sharp escalation in shelling on Kyiv's frontline with 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 that a Russian invasion of Ukraine is imminent, and Mr Macron's office had 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 Mr Putin and that Washington would seek a diplomatic solution until Russian "tanks are actually rolling".
Mr Macron also spoke with Mr Biden on the phone, with the White House saying they discussed the "ongoing diplomacy and deterrence efforts" over Russia's military build-up near Ukraine.
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During his 105-minute discussion with Mr Macron, Mr Putin said "the cause of the escalation is provocations carried out by the Ukrainian security forces," according to a Kremlin account.
Mr 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".
Mr 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".
Moscow has demanded that the NATO alliance permanently rule out Ukraine's bid for membership and the withdrawal of Western forces that deployed in eastern Europe since the end of the Cold War.
Mr Zelensky called for an immediate ceasefire and the resumption of talks under the Trilateral Contact Group of Russia, Ukraine and the OSCE.
"We stand for intensifying the peace process," he tweeted, adding that he had informed Macron about "new provocative shelling" on the frontline between Ukrainian forces and Russian-backed rebels.
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 20 February, allowing the Russians to head back to their bases.
The Belarus defence ministry said Mr 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.
Amid fears that Russia could use Belarus as a launch-pad for a lightning assault on Kyiv, exiled Belarus opposition leader Svetlana Tikhanovskaya said their extended stay was also a threat to the sovereignty of her own country.
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.
More bombardments were heard by AFP reporters overnight close to the frontline between government forces and the Moscow-backed rebels who hold parts of the 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."
Natalya Zibrova, a 48-year-old teacher, remained in her flat with her daughters, despite the shelling.
"We are all people. We all want to live normally," she said.
"I want to get up in the morning and think about how I will spend the day, and not to think about whether I and my children will have time to escape."
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," alleged 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'," the military chief of staff said.
The rebel regions have made similar claims about Ukraine's forces and have ordered a general mobilisation, while staging an evacuation of civilians into neighbouring Russian territory.
Mr Putin has also stepped up his rhetoric, reiterating demands for written guarantees that NATO roll back deployments in eastern Europe to positions from decades ago.
The volatile front line between Ukraine's army and the Russian-backed separatists has seen a "dramatic increase" in ceasefire violations, monitors from the OSCE 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.
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