NATO's troop build-up in Eastern Europe amid tensions with Russia over Ukraine could become permanent, the military alliance's top general said Tuesday.

NATO countries drew down their defense budgets following the end of the Cold War, as they started to look upon Russia as a partner, US General Philip Breedlove said.

But Russia's "annexation of Crimea... changes that dynamic," the NATO Supreme Allied Commander in Europe told a press conference, after meeting with Canada's Prime Minister Stephen Harper and other officials in Ottawa.

"What we are very clear about now is that that paradigm has changed in the current situation; Russia is not acting as a partner," Breedlove said.

"I think we need to look at our responsiveness, our readiness, and then our positioning of forces to be able to address this new paradigm that we have seen demonstrated in Crimea and now on the eastern border of Ukraine."

Pressed about whether the situation in Ukraine could result in a permanently beefed up NATO military presence in allied countries bordering Russia, he said: "I think this is something that we have to consider."

But that decision, he added, will be made by NATO leaders at an upcoming summit, where they will look into the question of whether they are correctly positioned in Europe.

The 28 members of the North Atlantic Treaty Organization have responded to Russia's intervention in Ukraine by stepping up defenses in Eastern Europe, sending warships, fighter jets and troops to the region.

The troop surge is scheduled to end on December 31.

Japan, NATO express concerns over Ukraine crisis
Brussels (AFP) May 06, 2014 - Japanese Premier Shinzo Abe and NATO head Anders Fogh Rasmussen agreed Tuesday the Ukraine crisis was a threat to global security which must be addressed.

As Russia rejected a new peace initiative and fears of open war mounted in Ukraine, Rasmussen said the situation amounted to the "gravest crisis to European security since the end of the Cold War."

The crisis is deepening in the run-up to May 25 elections, with some 40,000 Russian troops massed on the border with eastern Ukraine where the Kiev government is under pressure from pro-Kremlin militias.

"This is not just about Ukraine," Rasmussen said.

"This crisis has serious implications for the security and stability of the Euro-Atlantic area as a whole.

Abe said "we will tolerate any change to the status quo through intimidation, coercion or by force."

"This is not only applicable to Europe or Ukraine. This is applicable to east Asia ... this is applicable to the whole world," he said, adding: "We have to have a dialogue with Russia."

Both men stressed the importance of cooperation between NATO and Japan, which since World War II has had a 'Self Defence Force' with a limited role rather than an army which can be deployed abroad on military missions.

As such, Japan is not a member of the alliance but counts as a partner, working with it in counter-piracy and anti-terrorist efforts, as well as supporting its mission in Afghanistan.

Japan is however a close ally of the United States, with US President Barack Obama recently affirming those defence links as Tokyo views a rising China with alarm and concern.

Neither Abe, on the last leg of a European tour in Belgium, nor Rasmussen mentioned China by name.

Previously Rasmussen has stressed the need for a peaceful resolution of the many territorial disputes between Japan, China and their neighbours in Asia.