US Secretary of State Antony Blinken met Russian Foreign Minister Sergei Lavrov in Geneva last week. AFP
Tensions have soared over Russia's deployment of some 100,000 troops and heavy armour at its neighbour's borders, despite the Kremlin's insistence it is not planning a new incursion.
The United States and Britain ordered diplomats' families to leave Ukraine -- but both Kyiv and the European Union said the moves appeared premature amid divided views over how imminent any attack could be.
Top US diplomat Antony Blinken was to dial in to a meeting of EU counterparts in Brussels to brief them on his talks Friday with Russian Foreign Minister Sergei Lavrov, where the two sides failed to make a breakthrough but agreed to keep working to ease tensions.
The US is trying to marshal its allies to prepare an unprecedented package of sanctions for Moscow if its sends in more of its forces -- and European Union members insist they could hit the Kremlin with "massive consequences" within days if needed.
The US-led NATO alliances said its members were placing troops "on standby" and sending ships and jets to bolster eastern Europe's defences in response to the Russian buildup, pointing to recent decisions by Denmark, Spain and the Netherlands to mobilise forces.
"NATO will continue to take all necessary measures to protect and defend all allies," NATO chief Jens Stoltenberg said.
The Kremlin accused the alliance of ramping up tensions through "information hysteria" and "concrete actions", adding the risk of an offensive by Ukrainian troops against pro-Russia separatists was "very high."
EU foreign ministers will sound out Blinken over a written response Washington has committed to provide to Moscow this week after the Kremlin laid down a series of security demands that would stop Ukraine joining NATO and roll back the alliance's forces in eastern Europe.
The EU's foreign policy chief Josep Borrell said the bloc has as yet no plans to pull personnel out of Kyiv, adding there was no need to "dramatise" the situation while talks with Russia continued.
- 'Never seen before' -
The EU -- in consultation with the US and other allies -- is pushing to put together a package of sanctions against Moscow that it hopes will help deter Russia from any military action.
Foreign ministers are not expected to give approval to any options for sanctions on Monday, but an EU source said Russia's mammoth oil and gas supplies to Europe could be targeted.
"There's no doubt we are ready to react forcefully with comprehensive sanctions -- never seen before," Danish Foreign Minister Denmark FM Jeppe Kofod said.
The 27-nation bloc faces a complex task compiling its raft of measures as its members have starkly differing approaches and ties to Russia.
The new government in economic powerhouse Germany has faced criticism from Kyiv over its refusal to send arms to Ukraine and hesitation over calls to cut Moscow from the global SWIFT payment system.
German Foreign Minister Annalena Baerbock insisted any further aggression from Moscow would get a "clear response" from Europe and talked up economic support Berlin gives Kyiv.
European Commission chief Ursula von der Leyen said the bloc was preparing a 1.2-billion emergency financial aid package for Ukraine.
The West is struggling to work out at what point Russian actions would trigger the sweeping response it has threatened -- after US President Joe Biden spoke of a "minor incursion" last week.
Britain, which left the EU at the end of 2020, ramped up the rhetoric with Moscow over the weekend by alleging it had information the Kremlin was seeking to install a "pro-Russian" leader in Kyiv.
The current fears of a Russian invasion follow Moscow's 2014 annexation of Crimea from Ukraine.
Kyiv is already fighting a low-level conflict with Russian-backed rebels controlling a chunk of the east of the country that has claimed 13,000 lives in the past eight years.