Six Canadian CF-18 jets and dozens of military personnel have deployed for air patrols in Central and Eastern Europe aimed at reassuring NATO allies amid rising anxiety over Russia's territorial ambitions.

The departure came as the crisis in Ukraine deepened, events that the West blames on the Kremlin. Hundreds of pro-Russian separatists stormed government buildings across one of Ukraine's provincial capitals Tuesday and opened fire on police, a major escalation of the rebellion in defiance of new Western sanctions on Moscow.

But questions remain over the length and scope of Canada's mission that for now will include as many as 250 Canadian Armed Forces members joining the NATO response to the crisis in Ukraine.

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"There is a lot of uncertainty about what we're going to be doing over there," Lieutenant-General Yvan Blondin, commander of the Royal Canadian Air Force, told reporters as Canada's warplanes left Bagotville, Que., for Romania Tuesday morning. The fighters first headed to Iceland before receiving further direction on where they will be stationed in Romania, which borders Ukraine.

"As you can see … events are unfolding as we speak," Lt.-Gen. Blondin said. "We're not sure how long we are going to be staying, but we will be staying until the government tells us that it's time to come back."

Also heading to Romania are a C-17 heavy lift transport carrying spare parts and tools, as well as two Airbus jets, with one carrying as many as 80 Canadian Armed Forces members and the other tasked for refuelling the warplanes.

The CF-18s are supposed to conduct air policing and training exercises with North Atlantic Treaty Alliance countries including Romania, as tensions rise over Russia's efforts to destabilize Ukraine.

As of Tuesday night, Canada's National Defence department would not say where in Romania the CF-18s will be stationed, citing security concerns.

One government official said Canada's task in Europe remains somewhat undefined because the mission is NATO's and it will be up to the military alliance to decide on the scope and details of the undertaking.

Defence Minister Rob Nicholson said the CF-18s will help assuage concerns of NATO allies that border Russia. NATO has already stepped up air patrols in recent months across the Baltic states and other countries.

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"We are sending out a message to Russia and we are reassuring our allies that we are taking steps and making a point consistent with what NATO has been saying, the actions so far are unacceptable by Russia and we are sending out a very clear message," Mr. Nicholson told reporters.

Ukraine's beleaguered government has lost control of major parts of eastern Ukraine as insurgents have taken city halls, police stations and other government buildings in at least 10 cities and towns.

With reports from Associated Press and Reuters