Western leaders stepped up preparations for any Russian military action in Ukraine, with talks taking place on protecting energy supplies and US President Joe Biden saying he would consider imposing direct sanctions on President Vladimir Putin.
Tensions remained high after NATO said yesterday it was putting forces on standby and reinforcing eastern Europe with more ships and fighter jets in response to Russia's troop build-up near its border with Ukraine.
Russia, which denies planning an attack, said it was watching with "great concern". Kremlin spokesman Dmitry Peskov repeated Moscow's line that the crisis was being driven by US and NATO actions, not the Russian troop build-up.
In a televised address this evening, Ukrainian President Volodymyr Zelenskiy urged his compatriots to stay calm and said work was underway to bring about a meeting between him and the leaders of Russia, Germany and France.
"There are no rose-coloured glasses, no childish illusions, everything is not simple.... But there is hope," he said.
Mr Biden repeated that there were no plans to send US troops to Ukraine, which is not a NATO member, but said he would consider imposing direct sanctions on Mr Putin and that there would be "enormous consequences" if Russia invaded.
Reporters asked Mr Biden if he would see himself personally sanctioning Mr Putin if he invaded Ukraine.
"Yes," he said. "I would see that."
A US plane carrying military equipment and munitions landed in Kyiv today, the third shipment of a $200m security package to shore up Ukraine.
The US Defense Department has said about 8,500 US troops have been put on heightened alert and are awaiting orders to deploy to NATO's eastern flank. Mr Biden said today he may move the troops in the nearer term.
Western leaders say unity is paramount, though differences have emerged among European nations over how best to respond.
"It is absolutely vital that... the West is united now, because it is our unity now that will be much more effective in deterring any Russian aggression," British Prime Minister Boris Johnson told parliament, urging "our European friends" to be ready to deploy sanctions as soon as there was any incursion.
He said Britain was discussing with the United States the possibility of banning Russia from the SWIFT global payments system.
In Washington, senior Biden administration officials said the United States was in talks with major energy-producing countries and companies around the world over a potential diversion of supplies to Europe if Russia invades Ukraine.
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Speaking to reporters on a call, the officials did not name the countries or companies involved in discussions to protect supplies to Europe but said they included a broad range of suppliers, including sellers of liquefied natural gas (LNG).
"We've been working to identify additional volumes of non-Russian natural gas from various areas of the world; from North Africa and the Middle East to Asia and the United States," a senior administration official said, on condition of anonymity.
The EU depends on Russia for around a third of its gas supplies. Any interruptions to its Russian imports would exacerbate an existing energy crisis caused by shortages.
Russia has tens of thousands of troops near Ukraine and is demanding security guarantees from the West, including a promise by NATO never to admit Ukraine. Moscow sees the former Soviet republic as a buffer between Russia and NATO countries.
Speaking in Berlin, French President Emmanuel Macron said he would seek clarification over Russia's intentions towards Ukraine in a phone call with Mr Putin set for Friday.
Mr Macron and Germany's Chancellor Olaf Scholz reiterated that Moscow would pay a high price if it attacked Ukraine.
Political advisers from Russia, Ukraine, Germany and France are due to meet in Paris tomorrow under the so-called 'Normandy format' to seek ways of ending the conflict in eastern Ukraine between Kyiv's forces and pro-Russian separatists.
Mr Scholz defended Germany's refusal to follow other Western countries in sending Kyiv lethal weapons to defend itself against a possible Russian invasion, citing historical reasons for Berlin's caution.
So far, NATO has about 4,000 troops in multinational battalions in Estonia, Lithuania, Latvia and Poland, backed by tanks, air defences and intelligence and surveillance units.