Portugal Colonial - Diplomatic flurry to avert Russia-NATO clash over Ukraine

Also Monday, the German, Czech, Slovak and Austrian foreign ministers were expected in Kyiv, which has played down dire US warnings that Moscow had stepped up preparations for a major incursion into Ukraine.

US officials have said the Kremlin has assembled 110,000 troops along the border with its pro-Western neighbour but intelligence assessments have not determined whether President Vladimir Putin has actually decided to invade.

They said Russia is on track to amass a large enough force -- some 150,000 soldiers -- for a full-scale invasion by mid-February.

Such a force would be capable of taking the capital Kyiv in a matter of 48 hours in an onslaught that would kill up to 50,000 civilians, 25,000 Ukrainian soldiers and 10,000 Russian troops and trigger a refugee flood of up to five million people, mainly into Poland, the officials added.

On top of the potential human cost, Ukraine fears further damage to its already struggling economy.

And if Moscow attacks Ukraine it could face retaliation over the Nord Stream 2 pipeline -- set to double natural gas supplies from Russia to Germany -- with Berlin threatening to block it.

Russia is seeking a guarantee from NATO that Ukraine will not enter the alliance and wants the bloc to withdraw forces from member states in eastern Europe.

- 'Apocalyptic predictions' -

Moscow denies that it is planning to invade Ukraine, and Kyiv's presidency advisor said the chances of a diplomatic solution to the crisis remained "substantially higher than the threat of further escalation".

On Twitter, Ukraine's Foreign Minister Dmytro Kuleba sought to calm tensions, saying: "Do not believe the apocalyptic predictions. Different capitals have different scenarios, but Ukraine is ready for any development."

President Emmanuel Macron of France, which currently holds the rotating presidency of the EU, will be in Moscow on Monday and Kyiv on Tuesday to spearhead efforts to de-escalate the crisis.

He is expected to push forward a stalled peace plan for the festering conflict with Russian-backed separatists in eastern Ukraine.

The trip will be a political gamble for Macron, who faces a re-election challenge in April.

Also on Monday, German Chancellor Olaf Scholz will meet with Biden in Washington.

Biden has reacted to the Russian troop buildup by offering 3,000 American forces to bolster NATO's eastern flank, with a batch of the troops promised arriving in Poland on Sunday.

But US National Security Advisor Jake Sullivan told Fox News Sunday that Biden "is not sending forces to start a war or fight a war with Russia in Ukraine".

"We have sent forces to Europe to defend NATO territory," he said.

Scholz said Sunday that Berlin was prepared to send extra troops to the Baltics in addition to 500 soldiers already stationed in Lithuania under a NATO operation.

While he is in Washington, his foreign minister, Annalena Baerbock, will be in Kyiv along with her Czech, Slovak and Austrian counterparts for a two-day visit.

Scholtz will be in Moscow and Kyiv next week for talks with Putin and Ukrainian President Volodymyr Zelensky.

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T.Vitorino--PC