Fearing an invasion of Ukraine by Russia, dozens of countries are urging their citizens there to leave and are cutting back their diplomatic staff.
Among the countries that have called on their nationals to leave Ukraine are: the United States, Germany, Italy, Britain, Ireland, Belgium, Luxembourg, the Netherlands, Canada, Norway, Estonia, Lithuania, Bulgaria, Slovenia, Australia, Japan, Israel, Saudi Arabia and the United Arab Emirates.
The U.S. ordered the departure of most of its diplomatic staff in Kyiv, maintaining a consular presence in the western city of Lviv.
Russia added to the ominous tone by pulling some of its diplomatic staff out of Ukraine, with the Foreign Ministry saying Saturday its decision was prompted by fears of "possible provocations from the Kyiv regime."
The Dutch airline KLM announced Saturday that it was suspending its flights to Ukraine until further notice.
Ukraine's budget airline SkyUp said Sunday that its flight from Portugal to Kyiv was forced to land in Moldova because the plane's Irish leasing company had revoked permission for it to cross into Ukraine.
But the Ukrainian infrastructure ministry said Sunday the country would leave its airspace open despite the possibility of a Russian invasion.
Costs and speculation
Efforts to defuse the crisis in Ukraine via a frenzy of telephone diplomacy failed to ease tensions Saturday, with U.S. President Joe Biden warning that Russia faces "swift and severe costs" if its troops carry out an invasion.
Russian President Vladimir Putin slammed Western claims that Moscow was planning such a move as "provocative speculation" that could lead to conflict in the ex-Soviet country, according to a Russian readout of a call with French President Emmanuel Macron.
Speaking after new phone talks between Putin and Biden, the Kremlin's top foreign policy advisor Yury Ushakov told a conference call: "Hysteria has reached its peak."
"We don't understand why false information about our intentions is being passed to the media," Ushakov told reporters.
He said that Putin once again complained that the West has been arming Ukraine and that Kyiv authorities have been "sabotaging" Western-brokered peace agreements to end a years-long conflict in eastern Ukraine.
The Pentagon said Sunday that the latest top-level U.S.-Russian contacts did not provide "any cause for optimism" following the one-hour phone conversation Saturday between Biden and Putin.
U.S. national security adviser Jake Sullivan used some of the most specific — and chilling — language yet employed by an American official, warning that an invasion is "likely to begin with a significant barrage of missiles and bomb attacks... so innocent civilians could be killed."
That, he said, would be followed by a ground invasion in which "innocent civilians could get caught in the crossfire."
A Russian anti-submarine destroyer chased off a U.S. submarine during planned military drills near the Kuril Islands in the northern Pacific, forcing it to leave the country's territorial waters, Moscow said Saturday.
Russia’s Defense Ministry said it had summoned the U.S. defense attache in Moscow over the incident.
The U.S. military however denied the account, saying: "There is no truth to the Russian claims of our operations in their territorial waters."
Russia's Navy on Saturday launched large-scale exercises in the Black Sea even as Moscow dismissed as "hysteria" a U.S. warning that a Russian attack on Ukraine could begin within days.
Over 30 vessels from the Black Sea Fleet took to the sea from Sevastopol and Novorossiysk “to defend the coast of the Crimea peninsula ... from possible military threats," the military said.
As well as the naval exercises, large-scale Russian military drills are underway with the country's authoritarian ally Belarus, which lies just north of Ukraine and which also borders the European Union.
AFP contributed reporting.