This week's NATO summit will seek to deliver a strong message to Russian President Vladimir Putin of the alliance's willingness to defend its members – including the vulnerable Baltic States – against aggression. But the subtext of that statement will disappoint a Ukrainian government desperately appealing for help: NATO isn't coming to Kiev's rescue, no matter what Mr. Putin's armies and surrogates do in that country.

In an agenda-setting speech ahead of the crucial summit that begins Thursday in Wales, NATO deputy secretary general Alexander Vershbow said Russia's military moves in Ukraine had created a new solidarity and resolve to defend the alliance's borders. That new sense of purpose, he said, was reflected in a "Readiness Action Plan" that NATO leaders would announce this week, including the creation of a small "spearhead" force of several thousand troops that will be stationed in Eastern Europe and able to deploy to a crisis within 48 hours.

But, he made clear, that solidarity didn't extend to non-member Ukraine, where NATO says Russian troops and tanks are now directly aiding rebels in the east of the country. Asked if there was any "red line" Mr. Putin could cross that would prompt NATO involvement in the country, Mr. Vershbow left no doubt that Ukraine would have to fight alone.

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"I don't see any red line that, if crossed, would lead to military engagement" in Ukraine, he told a "NATO after the Wales Summit" seminar hosted by Cardiff University. Ukrainian President Petro Poroshenko will attend this week's NATO meeting as a non-member observer.

"Ukraine understands that they're not a beneficiary of an Article 5 [NATO collective defence] guarantee," Mr. Vershbow told The Globe and Mail afterwards. "But I think we will show solidarity with Ukraine, meeting with Poroshenko. We'll roll out some of the assistance that we've been working on for Ukraine… it may not be everything that everybody wants, but again NATO is not the only responder. The broad international message from NATO, from the EU, from other actors, hopefully will make a difference."

Mr. Poroshenko asked last week that Ukraine be considered for full membership in NATO, but the request has been met with stony silence from the alliance, which is still seeking to avoid a direct military confrontation with Russia.

The EU, Canada and the United States have collectively imposed escalating sanctions on Russia in response to its actions in Ukraine. But while those measures are taking an economic toll – the Russian economy contracted in both June and July – they have not demonstrably affected the Kremlin's behaviour.

NATO believes that 100 battle tanks, accompanied by at least 1,000 infantry, entered eastern Ukraine last week. The column has reportedly pushed towards the Azov Sea port of Mariupol, creating a new front in the conflict and relieving the pressure on pro-Russian rebels who had been surrounded and facing defeat in Donetsk and Lugansk.

Russia also annexed the Crimean Peninsula from Ukraine in March, following a controversial referendum there. Moscow was infuriated by the February ousting of the Kremlin-friendly government of Viktor Yanukovych, and accuses Western governments of supporting an illegal "coup" in Kiev.

Mr. Vershbow spoke hours after it became public that Mr. Putin had told European Commission President Jose Manuel Barroso that Russia "could take Kiev in two weeks" if it wanted. The Kremlin said Tuesday that Mr. Putin's remarks had been "misinterpreted," but didn't deny the quote.

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Separately, a senior Kremlin official said Tuesday that Russia would soon adjust its military doctrine in response to the increased NATO presence in Eastern Europe.

"[NATO plans to] stir up its military activities, take measures on providing long-term presence of NATO military units in Eastern Europe," Mikhail Popov, deputy chairman of the Russian Security Council, told the official RIA Novosti news service. "It's clear to everyone against whom these measures are directed."

Mr. Vershbow – who was U.S. ambassador to Moscow during Mr. Putin's early years in power – said the best outcome for Ukraine might now be a "fair" negotiated solution that took Russia's interests into account without violating Ukraine's sovereignty.

The other keynote speaker at the Cardiff University seminar warned that NATO needed to accept that it cannot achieve its aims in Ukraine, and avoid making empty promises to Mr. Poroshenko.

Stephen Krasner, a former top U.S. State Department official, said the alliance should focus on providing the Baltic States of Estonia, Latvia and Lithuania, tiny former republics of the Soviet Union that joined NATO in 2004, with credible deterrent against any aggression. Mr. Putin has claimed the right to "defend" Russian-speakers abroad, and Estonia and Latvia have significant Russian-speaking populations.

"We can't pretend we're going to defend Ukraine, when we can't do that," said Prof. Krasner, who now teaches at Stanford University. But, he said, "there are real reasons for us to fight in the Baltic States."

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He called for NATO troops to be deployed along Estonia's and Latvia's borders with Russia in much larger numbers than the 4,000-soldier rapid deployment force apparently under consideration at this week's summit, which he said would be too small to counter the massive military might Russia has deployed along its western frontier. At one point during the crisis, Russia brought 150,000 troops to its border with Ukraine for snap "exercises."

Stephen Harper is heading to a crucial summit of NATO leaders where the Western military alliance will give itself the power to respond to threats more quickly in the face of Russia's continued effort to destabilize and break up Ukraine. However, the Harper government is balking at a push for NATO countries to boost military spending to at least 2 per cent of gross domestic product. Here is a look at how Canada's defence spending compares to other NATO countries.

NATO member defence spending

Chart shows defence expenditures as a percentage of GDP for 2013 (Current Prices)

SOURCE: NATO