NATO troops arrive at the site of a suicide car bomb attack in Kabul
NATO troops arrive at the site of a suicide car bomb attack in Kabul August 10, 2014. Reuters

NATO has sent its regrets to Ukraine and advised the country it would need to fight off Russia's aggression on its own. The reason is plain and simple - Ukraine is a non-member state.

Regardless of how much Russia escalates its ambitious invasion and expansion plans, Ukraine would have to fight alone, NATO deputy secretary general Alexander Vershbow said.

"Ukraine understands that they're not a beneficiary of an Article 5 [NATO collective defence] guarantee," Vershbow told The Globe and Mail.

On Tuesday, Olexander Scherba, ambassador-at-large at the Ukrainian foreign ministry, expressed exasperation over the Western countries' disregard for Ukraine's sovereign democracy.

Read: West is 'Really Weak' vs Russia, Says Ukrainian Diplomat; Crisis Has Displaced Over 1M People

Vershbow, however, tried to douse water into those burning frustrations and said NATO will try to send assistance to Ukraine and its troops but "it may not be everything that everybody wants."

Although Ukraine had asked to lodge a full membership application in NATO, the alliance had yet to fully consider this, as it seeks to avoid a direct military confrontation with Russia.

Russian President Vladimir Putin had earlier warned Ukraine's defenders, dangling the threat of a nuclear war.

Read: Ukraine Crisis: Putin Dangles Nuclear War Threat, US Senators Advise Sending Defensive Weapons

Moreover, Mr Putin had told European Commission President Jose Manuel Barroso that Russia "could take Kiev in two weeks" if it wanted.

With Vershbow's admission, Stephen Krasner, a former top U.S. State Department official, said the alliance should stop making empty promises to Ukraine.

"We can't pretend we're going to defend Ukraine, when we can't do that," the Globe and Mail quoted Krasner, as he reminded "there are real reasons for us to fight in the Baltic States."

These Baltic States are Estonia, Latvia and Lithuania, former republics of the Soviet Union that joined NATO in 2004.

Meantime, a sense of panic has enveloped the Ukraine port city of Mariupol as residents feared it is stationed to become the next battleground in the Ukraine crisis.

Residents have started digging trenches to prepare the city from a potential attack, a report by the LA Times said.

"Everybody in the city is mobilizing for this war," Marina Odnorog, a volunteer for New Mariupol organization, said.

Mariupol is regarded as an important factor in eastern Ukraine's economy because it holds several large metallurgy plants and a large port on the Sea of Azov.