WASHINGTON — British Prime Minister David Cameron has warned European leaders against repeating the historic pre-World War II blunder of appeasement instead of resisting Russian belligerence in Ukraine.

Cameron invoked the sellout by British Prime Minister Neville Chamberlain to Hitler at Munich while urging his counterparts at a closed-door meeting Saturday to stand firm against Russia’s meddling in Ukrainian territory, the Italian newspaper La Repubblica said.

“We run the risk of repeating the mistakes made in Munich in 1938. We cannot know what will happen next,” Cameron was reported as saying in Brussels.

“This time we cannot meet Putin’s demands. He has already taken Crimea and we cannot allow him to take the whole country.”

Cameron’s visceral warning came as President Obama jetted to Estonia, where he will deliver a speech Wednesday intended to solidify the “steadfast” commitment of the United States to the Baltic states on Russia’s border, the White House said.

NATO obligations commit members to mutual defense, but Ukraine isn’t part of NATO.

Even German Chancellor Angela Merkel, the main mediator with Putin, was reported to be furious with the Russian leader, calling him “irrational and unpredictable.”

The heightened concern comes after Putin told a European official: “We could take Kiev in two weeks.”

The Kremlin didn’t deny the remark after it was reported, but slammed European Commission President José Manuel Barroso for leaking it.

“Whether these words were said or not, in my viewpoint, the quote given is taken out of context, and it had an absolutely different meaning,” said Kremlin official Yuri Ushakov.

It was just the latest bellicose rhetoric from the Russian leader. Last week, Putin noted Russia’s nuclear arsenal and declared: “It’s best not to mess with us.”

The influx of Russian armor, equipment and military personnel was having a major impact on the ground in Ukraine.

Separatist rebels made gains in Donetsk, the biggest city under their control, and were on the verge Tuesday of recapturing an airport that the Ukrainian military had retaken two months earlier.

A spokesman for Ukraine’s National Security Council said Russian troops have been seen in Donetsk, Luhansk and other locations throughout eastern Ukraine.

NATO officials meeting in Wales this week are set to propose a new rapid-reaction force of 4,000 soldiers to protect Eastern Europe.