Ukraine’s president played down intensified warnings of a possible Russian invasion within days, saying he had yet to see convincing evidence, even as the US warned Sunday of more Russian troops pressing closer to Ukraine’s borders and some airlines cancelled or diverted flights there.

The White House said President Joe Biden would talk later in the day with Ukrainian President Volodymyr Zelenskyy.

The Ukrainian leader’s repeated statements urging calm among his people — while Russian forces surround Ukraine on three sides in what Russia insists are military exercises — grew this weekend to Zelenskyy questioning strident warnings from US officials in recent days that Russia could be planning to invade as soon as midweek.

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The US picked up intelligence that Russia is looking at Wednesday as a target date, according to a US official familiar with the findings. The official, who was not authorised to speak publicly and did so only on condition of anonymity, would not say how definitive the intelligence was.

“We’re not going to give Russia the opportunity to conduct a surprise here, to spring something on Ukraine or the world,” Jake Sullivan, the US national security adviser, told CNN on Sunday, about the US warnings.

“We are going to make sure that we are laying out for the world what we see as transparently and plainly as we possibly can,” he said.

The US largely has not made public the evidence it says is underlying its most specific warnings on possible Russian planning or timing.

The Russians have deployed missile, air, naval and special operations forces, as well as supplies to sustain an invasion. This week, Russia moved six amphibious assault ships into the Black Sea, augmenting its capability to land on the coast.

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Pentagon spokesman John Kirby said Sunday that Russia had well over 100,000 troops along Ukraine’s borders, “and actually, over the last few days, even more.” Kirby cited “a mosaic of intelligence” the US had gathered, but gave no details. “We have good sources of intelligence and they’re telling us that, you know, that things are sort of building now to some crescendo opportunity for Mr. Putin.”

Zelenskyy’s comments this weekend indicated frustration at the warnings from Washington, as he tries to minimizes damage to Ukraine’s economy during the crisis.

“We understand all the risks, we understand that there are risks,” he said in a live broadcast. “If you, or anyone else, has additional information regarding a 100% Russian invasion starting on the 16th, please forward that information to us.”

In an hourlong call Saturday with Russian President Vladimir Putin, Biden said an invasion of Ukraine would cause “widespread human suffering” and that the West was committed to diplomacy to end the crisis but “equally prepared for other scenarios,” the White House said. It offered no suggestion that the call diminished the threat of an imminent war in Europe.

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Reflecting the West’s concerns, Dutch airline KLM has canceled flights to Ukraine until further notice, the company said.

Dutch sensitivity to potential danger in Ukrainian airspace is high following the 2014 shooting down of a Malaysian jetliner flying from Amsterdam to Kuala Lumpur as it flew over a part of eastern Ukraine held by Russia-backed rebels. All 298 people aboard died, including 198 Dutch citizens.

The Ukrainian charter airline SkyUp said Sunday its flight from Madeira, Portugal, to Kyiv was diverted to the Moldovan capital of Chisinau after the plane’s Irish lessor said it was banning flights in Ukrainian airspace.

Ukrainian presidential spokesman Serhii Nykyforov told The Associated Press that Ukraine has not closed its airspace.

But Ukraine’s air traffic safety agency Ukraerorukh issued a statement declaring the airspace over the Black Sea to be a “zone of potential danger” and recommended that planes avoid flying over the sea Feb. 14-19.

The Putin-Biden conversation, following a call between Putin and French President Emmanuel Macron earlier in the day, came at a critical moment for what has become the biggest security crisis between Russia and the West since the Cold War. US officials believe they have mere days to prevent an invasion and enormous bloodshed in Ukraine.

German Chancellor Olaf Scholz will fly to Kyiv on Monday and Moscow on Tuesday to meet with the presidents in those capitals.