NATO's top military commander in Europe said on Monday he no longer thought regular Russian troops would enter eastern Ukraine, predicting Moscow could achieve its goals through the unconventional forces stirring up trouble there.

U.S. air force Gen. Philip Breedlove said it was a completely false Russian narrative that it was only Ukrainians rebelling in the east of their country, saying it was clear that special forces troops from Russia were operating there as they did in Crimea before its annexation.

"Remember that [Russian President Vladimir] Putin denied their presence and now he has admitted to their presence in Crimea. The same thing will come out of Ukraine as time rolls out," he told a military and diplomatic audience in Ottawa.

Breedlove is embarking on two days of talks with Canadian political and military leaders just as heavy clashes erupt between Ukrainian and pro-Russian forces in Ukraine's eastern region.

He met briefly with Prime Minister Stephen Harper, Defence Minister Rob Nicholson and Chief of the Defence Staff Gen. Tom Lawson.

"Exactly what we saw in Crimea is being mirrored in eastern Ukraine," added Breedlove.

Russia setting stage for separatist movement

Russia has massed tens of thousands of troops on its border with eastern Ukraine, prompting fears that Moscow might send ground forces in to protect the rights of ethnic Russians.

Breedlove said that until a week ago, he thought the most likely military response from Russia would be to send in troops to southern Ukraine and secure a land bridge to the peninsula of Crimea — which voted in March to join Russia — before possibly pushing on toward the Black Sea port of Odesa and then farther west toward Moldova.

"Today I would tell you I don't think that's the most likely course of action ... I think now that Putin may be able to accomplish his objectives in eastern Ukraine and never go across the border with his forces," he said.

"Now I think probably the most likely course of action is that he will continue doing what he's doing — discrediting the government, creating unrest, trying to set the stage for a separatist movement," and that would make it easier to cement Moscow's military and economic hold on eastern Ukraine, Breedlove added.

"In that case, I think it's the most troublesome for NATO because if the forces do not come across the border, my guess is that many will want to try to quickly go back to business as usual, and I, for one, do not believe annexing Crimea is business as usual."

'Slow-motion invasion'

Shortly before his public remarks, Breedlove discussed Ukraine and Russia in a meeting with Harper, who told reporters beforehand that Russia was mounting a "a slow-motion invasion" of Ukraine.

The Prime Minister's Office had invited cameras into the meeting but said no questions from reporters would be allowed.

The meetings are being held as Ukraine's elite troops have been dispatched to quell unrest in the key southern port city of Odesa.

Harper said the latest developments are "very deeply concerning" and that NATO has asked for Canada's support.

"We are obviously concerned by the continuing escalation of violence in Ukraine, which to me very much appears to be clearly, what I would call, a slow-motion invasion on the part of the Putin regime," Harper said, seated next to Breedlove in the prime minister's Langevin Block office.

Frigate, planes dispatched

Harper noted Canada has contributed air, naval and army assets, and that this was done to give assurances to Canada's eastern European allies of its support.

Stephen Harper meets with NATO's Gen. Philip Breedlove

Prime Minister Stephen Harper, right, meets with U.S. Gen. Philip Breedlove, NATO's supreme commander in Europe, in Ottawa May 5, 2014. (CBC)

Pitched battles between pro-Russian militants and Ukrainian forces took place in and around the city Slovyansk, which has been a hotbed of unrest.

Breedlove is expected to give Canadian authorities an update on NATO's reassurance package for eastern European countries bordering the troubled region.

Canada has dispatched a frigate to operate with NATO's standing task force in the eastern Mediterranean Sea; six CF-18 fighters to operate out of a Romanian air base; and will deploy troops from the 3rd Battalion Princess Patricia's Canadian Light Infantry to take part in a land exercise in Poland. 

With files from The Canadian Press