While Russia continued to push Ukrainian forces out of Crimea, NATO and Ukraine issued warnings on Sunday about the buildup of Russian troops along Ukraine's eastern border.

The Washington Post reports that NATO's supreme allied commander Europe, U.S. Air Force Gen. Philip Breedlove, said Russia had "assembled a large force ... that could pose a threat to Moldova's separatist Transnistria region."

The Post adds:

" 'The [Russian] force that is at the Ukrainian border now to the east is very, very sizeable and very, very ready,' Breedlove said at an event sponsored by the German Marshall Fund.

"Ukraine's east is also considered under threat; Ukrainian officials have been warning for weeks that Russia is trying to provoke a conflict there, a charge Russia denies.

"But Breedlove said Russian ambitions extend beyond Ukraine.

" 'There is absolutely sufficient force postured on the eastern border of Ukraine to run to Transdniestria if the decision was made to do that and that is very worrisome,' Breedlove said."

Moscow is denying that there is any troop buildup. Russia Today, a government-funded English language news service, reports that Russian Deputy Defense Minister Anatoly Antonov said the issue has even been discussed with Defense Secretary Chuck Hagel.

Antonov also invited international observers to verify his claims.

"Russian Armed Forces are not undertaking any undeclared military activity that would threaten the security of neighboring countries," Antonov said.

Meanwhile, Ukraine's acting foreign minister tells ABC News' This Week the chance of war with Russia is "becoming higher."

"The problem is that Russians, and particularly the — Putin's administration — Putin himself is not talking to the rest of the world, he doesn't want to listen to the world, he doesn't want to respond on the arguments ... to deescalate [the] situation and stop invasion," Andrii Deshchytsia told ABC. "We don't know what Putin has in his mind and what will be his decision."

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