Russia's strategic nuclear forces have held exercises overseen by President Vladimir Putin as Washington accuses Russian troops massed near Ukraine's border of advancing and being "poised to strike".
With Western fears of war rising, foreign ministers from the G7 group of rich nations said they had seen no evidence Russia is reducing its military activity in the area and remained "gravely concerned" about the situation.
After Kyiv and Moscow traded accusations over new shelling near the border, France and Germany urged all or some of their citizens in Ukraine to leave. United States Defense Secretary Lloyd Austin said Russian forces were beginning to "uncoil and move closer" to the border.
"We hope he (Putin) steps back from the brink of conflict," Mr Austin told a news conference in Lithuania, saying an invasion of Ukraine was not inevitable.
Russia ordered the military build-up while demanding NATO prevent Ukraine from ever joining the alliance but says Western warnings that it is planning to invade Ukraine are hysterical and dangerous. Moscow says it is pulling back, but Washington and allies say the build-up is mounting.
Washington and NATO say Moscow's main demands are non-starters, but in Ukraine fears are growing over Mr Putin's plans.
Venting his frustration at a security conference in Munich, Ukrainian President Volodymyr Zelensky said the global security architecture was "almost broken".
Mr Zelensky travelled to Munich despite shelling in his country's conflict-torn east that left two Ukrainian soldiers dead.
He urged the permanent members of the UN Security Council, Germany and Turkey to meet to draw up new security guarantees for his country.
"The rules that the world agreed on decades ago no longer work," Mr Zelensky said. "They do not keep up with new threats ... This is a cough syrup when you need a coronavirus vaccine."
Mr Zelensky on Saturday described his country was a "shield" against Russia that deserved more support in the face of a feared invasion.
He condemned "a policy of appeasement" towards Moscow.
"For eight years, Ukraine has been a shield," Mr Zelensky said.
"For eight years, Ukraine has been holding back one of the greatest armies in the world," he added.
Mr Zelensky called for "clear, feasible timeframes" for Ukraine to join the US-led NATO military alliance.
The conference is taking place as Russian troops stand amassed on the Russian, Belarusian and Crimean borders to Ukraine. Source: Getty Images Europe
The Ukrainian leader also said he was willing to meet with Vladimir Putin, to find out "what the Russian president wants".
Mr Zelensky also pushed back against Washington's dire predictions in Munich.
"We do not think that we need to panic," he told the audience of top-level officials and security experts from around the world.
World Bank President David Malpass told Mr Zelensky on Saturday the bank was readying funding to Ukraine of up to $US350 million ($A488 million).
The Kremlin said Russia successfully test-launched hypersonic and cruise missiles at sea during the nuclear forces drills. Mr Putin observed the exercises on screens with Belarusian leader Alexander Lukashenko from a "situation centre".
US President Joe Biden said on Friday he believed Putin would invade Ukraine in the coming days and Mr Austin said the exercises were stoking concerns around the world.
G7 foreign ministers called on Russia to choose the path of diplomacy. "As a first step, we expect Russia to implement the announced reduction of its military activities along Ukraine's borders. We have seen no evidence of this reduction," they said in a statement.
Mr Zelensky said he had an "urgent" phone conversation with French President Emmanuel Macron and discussed possible ways of immediate de-escalation and political-diplomatic settlement. Mr Macron is due to speak with Putin on Sunday.
The nuclear drills follow manoeuvres by Russia's armed forces in the past four months that have included a build-up of troops - estimated by the West to number 150,000 or more - to the north, east and south of Ukraine.
New helicopters and a battle group deployment of tanks, armoured personnel carriers and support equipment have been moved to sites in Russia near the border, according to US-based Maxar Technologies, which tracks developments with satellite imagery.
Moscow-based analysts said Saturday's exercises were aimed at sending a message to take Russia's demands seriously.
"Ignoring Russia's legitimate rights in this area adversely affects the stability not only on the European continent, but also in the world," Russian Foreign Minister Sergei Lavrov was quoted by his ministry as telling his French counterpart by phone.
A NATO official said the alliance relocated staff from Kyiv to the western city of Lviv and to Brussels for safety reasons. The United States and other countries have moved diplomats to Lviv.
Russian-backed rebels seized a swathe of eastern Ukraine and Russia annexed Crimea from Ukraine in 2014. Kyiv says more than 14,000 people have been killed in the conflict in the east.
Separatist leaders in eastern Ukraine have declared a full military mobilisation after ordering women and children to evacuate to Russia, citing the threat of an imminent attack by Ukrainian forces, which Kyiv denied.
Kyiv and Western leaders say the mobilisation, evacuation and increased shelling are part of a Russian plan to create a pretext for an invasion.
Strategic missile tests
The increasingly fraught warnings of an invasion, intense clashes in Ukraine's east and the evacuation of civilians from Russian-backed rebel regions have further heightened fears of a major conflict in Europe after weeks of tensions.
The Kremlin insists it has no plans to attack its neighbour, but Moscow has done little to reduce tensions, with state media accusing Kyiv of plotting an assault on rebel-held pro-Russia enclaves in eastern Ukraine.
Saturday's exercises of strategic forces saw Russia test-fire its latest hypersonic, cruise and nuclear-capable ballistic missiles.
The United States insists that, with around 150,000 Russian troops on Ukraine's borders - as many as 190,000, when including the Russian-backed separatist forces in the east - Moscow has already made up its mind to invade.
Some of the Russian forces, around 30,000 troops, are in Belarus for an exercise which is due to end on Sunday. Moscow has said these forces will return to barracks, but US intelligence is concerned that they could take part in an invasion of Ukraine.
Map showing positions of Russian troops around Ukraine. Source: SBS News
Russia has announced a series of withdrawals of its forces from near Ukraine in recent days, saying they were taking part in regular military exercises. It has dismissed western claims of an invasion plan as "hysteria".
But Putin has also stepped up his rhetoric, reiterating demands for written guarantees that Ukraine will never be allowed to join NATO and for the alliance to roll back deployments in eastern Europe to positions from decades ago.
'Dramatic increase' in clashes
The volatile frontline between Ukraine's army and separatists in the breakaway regions of Donetsk and Lugansk has seen a "dramatic increase" in ceasefire violations, international monitors from the OSCE European security body 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 the lives of more than 14,000 people.
The OSCE said Saturday there had been 1,500 ceasefire violations in Donetsk and Lugansk in just one day.
Ukraine's army and separatist forces traded accusations of fresh shellfire on Saturday, with Kyiv saying two of its soldiers had died in a shelling attack, the first fatalities in the conflict in more than a month.
A dozen mortar shells fell within a few hundred metres (yards) of Ukraine's interior minister Denys Monastyrskiy on Saturday as he met journalists on a tour of the frontline.
The rebels declared general mobilisations in the two regions, calling up men to fight even as they announced mass evacuations of women and children into Russia.
A representative of the Lugansk Peoples Republic in the Joint Centre for Control and Coordination registers shelling fragments in the village of Mykolaivka. Source: AAP
Moscow and the rebels have accused Kyiv of planning an assault to retake the regions, claims fiercely denied by Ukraine and dismissed by the West as part of Russian efforts to manufacture a pretext for war.
Ukrainian Foreign Minister Dmytro Kuleba denounced reports of Ukrainian shells falling on Russian territory as "fake".
Germany and France on Saturday urged their citizens to leave Ukraine.
Both German airline Lufthansa and Austrian Airlines said they would stop flights to Kyiv and Odessa from Monday until the end of February, but would maintain flights to western Ukraine.
