Russia's Ukraine "operation" has backfired by making its former vassal state more pro-Western than ever, a U.S. diplomat has said.

"They [Russian leaders] are driving the Ukrainian people away from their historic relationship with Russia," Kurt Volker, the US state department's special envoy on Ukraine, told press in Brussels on Thursday, according to EUObserver.

"Ukraine today is more unified, more nationalist, more oriented toward Europe and Nato and the West than has even been true before, and that's a direct result of Russia's intervention in Ukraine and killing of Ukrainians," he said.

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Russia's actions were putting the 1.5 million or so mostly Russian-speaking Ukrainians who still lived there through a "horrific experience", Volker noted.

"The ceasefire continues to be broken every night, people continue to be killed ... there's shelling, mortar fire, sniper fire, unexploded ordinance, no freedom of movement, a collapsing economy, threats to water supply, food insecurity, pressure on healthcare," he said.

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Russian president Vladimir Putin has denied Russia's involvement in the fighting, which erupted in 2014 after Ukrainians toppled a pro-Russian government in Kyiv, but Kremlin propaganda had convinced few people in Europe or the U.S., Volker indicated.

"This is purely a Russia-controlled operation, as opposed to any kind of indigenous conflict," he said.

The U.S. and EU have asked Russia to extract its forces, return control of the border to Ukraine, and let in UN peacekeepers to protect the general population.

Putin is willing to let in a mini-UN mission to protect international observers from the Organization for Security and Co-operation in Europe (OSCE), who already patrol the line of contact.

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But Volker said the U.S. and EU states would not back that in the UN Security Council, as it would merely entrench the position of the Russia-controlled breakaway 'republics' in the Donetsk and Luhansk regions.

The looming split of the Ukrainian orthodox church from the Russian one underlined Volker's claim that Putin had lost Ukraine in political terms.

"I hope there are no protests or violence instigated [in Ukraine] as a result of this decision [Ukrainian autocephaly] - that would be tragic," Volker said.

Opinion polls also backed up his claim, with two-thirds of Ukrainians now keen to join NATO, compared to less than half before Russia's invasion.

"It's very important that we [the US and EU] continue to keep sanctions in place, given that Russia has not withdrawn its forces from Ukraine," Volker said, referring to Western economic sanctions, visa bans, and asset freezes on Russia.

He last met Russia's envoy on the conflict, Vladimir Surkov, in January and had no plans to meet again, but the two communicated via "notes" despite the frozen diplomacy, Volker said.