Ukraine's sovereignty over the southern region of Crimea appeared to be under threat Wednesday, as Russian-backed fighters moved dozens of kilometres outside their base in this Black Sea port, establishing a checkpoint on the main road connecting Sevastopol to the regional capital.

President Vladimir Putin also ordered the Russian military in its central and western commands – more than 150,000 troops with hundreds of tanks and helicopter gunships – to be put on alert for war games in the areas bordering Ukraine. Russian Defence Minister Sergei Shoigu characterized the manoeuvre as a snap military drill, similar to others Mr. Putin has ordered in the past in other parts of the country.

But the timing of the military moves raised already sky-high tensions in Ukraine, as well as suspicions that Russia is considering some form of intervention in this former Soviet republic, and prompted warnings from U.S. officials against any intervention.

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The Globe and Mail saw at least a dozen men wearing fatigues – supported by an armoured personnel carrier – standing under a Russian flag at a checkpoint erected roughly halfway along the 80-kilometre road from Sevastopol to Simferopol, putting it close to the administrative border that separates the Sevastopol municipality from the rest of Crimea and Ukraine.

The men, some wearing balaclavas, used flashlights to look inside each vehicle approaching Sevastopol. They reportedly later told journalists they were local "volunteers."

Earlier Wednesday, at least two armoured personnel carriers were seen manoeuvring in the centre of this port city, which has historic ties to Russia and hosts Russia's Black Sea Fleet under an agreement between Moscow and Kiev. Mr. Shoigu said the Kremlin was "carefully watching what is happening in Crimea" and would take "measures to guarantee the safety of facilities, infrastructure and arsenals of the Black Sea fleet."

Mr. Shoigu said the drills will last until March 3. Russia has so far refused to recognize the regime that came to power in Kiev following the violent ouster of Moscow-backed Viktor Yanukovych. Meanwhile, the West is rushing to support it, with Washington and Brussels giving vocal support – and promising money – to the protest movement that overthrew an elected government. Foreign Minister John Baird is also rushing to Kiev this week, aiming to show Canada's solidarity with interim president Oleksander Turchynov and the prime minister-designate Arseniy Yatseniuk.

President Barack Obama warned "outside actors in the region … to end provocative rhetoric and actions." Instead, Moscow should use its "influence in support of unity, peace and an inclusive path forward," Josh Earnest, a White House spokesman said.

Many here in Crimea, however, say they would welcome Russian intervention. While many of the revolutionaries in Kiev are Ukrainian-speakers who want to see the country take steps towards joining the European Union, many Crimeans see themselves as Russians who were left outside the borders of their motherland when the Soviet Union fell apart.

Thousands of ethnic Russians rallied Wednesday outside the regional parliament building in Simferopol, shouting for deputies to call a referendum about seceding from Ukraine and possibly joining Russia. Deputies had been expected to introduce some kind of resolution on Wednesday regarding Crimea's future, but they were blocked by thousands of ethnic Tatars who say they want to remain in Ukraine. Minor clashes broke out, and one person died of a heart attack, before parliament agreed to postpone any vote on secession.

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"We don't want to be with Ukraine. … Sevastopol, Kerch and Simferopol all want to join Russia," said Darya Artyomenko, a 23-year-old law student who attended the Simferopol rally. Her voice was barely audible above chants of "Russia!" and "Referendum!" Ms. Artyomenko said she didn't want to live in a country controlled by "fascists" from western Ukraine whom she believes are intent on eliminating the Russian language and culture.

In Brussels, North Atlantic Treaty Organization defence ministers ignored Russia's war-games alert and called for co-operation in Ukraine's unfolding crisis. The Western alliance, which includes Canada, said it supported "Ukrainian sovereignty and independence, territorial integrity, democratic development, and the principle of inviolability of frontiers." NATO has invited Ukraine to join the military alliance – a move bitterly opposed by Russia.

Russian-speakers in the east and south of the country were angered that one of the first actions taken by the post-revolution parliament in Kiev was to repeal a law, adopted under the toppled Mr. Yanukovych, that allowed regions like Crimea to adopt Russian as an official second language, alongside Ukrainian.

"Nobody asked south Ukraine if we want this new government," said Svetalana Khromova, a 36-year-old childcare worker who joined the Simferopol demonstration. "We've lived here for 200 years. We've always spoken Russian and we'll keep speaking Russian."

While many Russian-speakers feel threatened by the idea of living under the new government in Kiev, other ethnic groups say they have no interest in seeing Crimea join Russia.

The pro-Russian demonstration in Simferopol was countered by thousands of Crimean Tatars, who are Muslims and speak a Turkic dialect. They blocked the doors of parliament and kept the regional assembly from meeting. Mixing chants of "Glory to Ukraine!" with "God is great!" the Tatars claimed a victory Wednesday when they forced the parliament to call of its planned session.

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Many of Ukraine's 300,000 Crimean Tatars associate Russian rule with the Soviet period, which saw the entire population was deported en masse by Joseph Stalin in 1944. Many only returned to Crimea after the fall of the Soviet Union and the birth of independent Ukraine in 1991.

"We don't expect anything good from Russia," said 52-year-old Ibazir Ilyasov. "Ukrainian nationalists and Crimean nationalists have the same enemy: Russia."

Ethnic Russians make up about 58 per cent of Crimea's two million residents. Ukrainians make up 24 per cent, while Crimean Tatars are 12 per cent. In Sevastopol, ethnic Russians make up 70 per cent of the city's population of 340,000.

With a report from Paul Koring in Washington

Follow us on Twitter: @markmackinnon @PaulKoring