28 February 2014 Last updated at 09:42 ET By Jonathan Marcus BBC diplomatic correspondent
Recent developments look much like the preliminary to the Russian assault on Georgia in 2008
Nobody yet knows who the armed men at Simferopol airport are
Recent developments look much like the preliminary to the Russian assault on Georgia in 2008
Could Russia intervene militarily in Crimea to safeguard its strategic interests? Or, to put the question a different way, has Russia already intervened?
Nobody yet knows the identities of the armed men who seized control of Simferopol airport.
But their equipment, their vehicles and their behaviour all signal that this is a trained military unit, not a rag-tag group of pro-Russian loyalists.
"These men look like a formed and organised body of troops. They appear to be disciplined, confident and uniformly dressed and equipped," says Brigadier Ben Barry, a land warfare expert at the International Institute for Strategic Studies in London.
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Crimea
- Autonomous republic within Ukraine
- Transferred from Russia in 1954
- Ethnic Russians - 58.5%
- Ethnic Ukrainians - 24.4%
- Crimean Tatars - 12.1%
Source: Ukraine census 2001
"Irregular militia may obtain bits of official kit but they tend to look like a military jumble sale."
All we know is that what looks to be a military unit has secured the airport in Simferopol, the Crimean regional capital.
This comes against a background of deepening tensions, with the Russians working through a predictable play-book of threats and menaces aimed at the new interim authorities in Ukraine.
Combat aircraft in areas bordering Ukraine are on alert. Snap military exercises have been held to demonstrate the readiness of Russian forces.
Misleading comparisons
There have been economic threats too, for example to increase customs duties at the two countries' border along with widespread rhetoric warning of the threats to Russian minorities, orthodox religious shrines and so on.
Nobody yet knows who the armed men at Simferopol airport are
So far, it looks much like the preliminaries to the Russian assault on Georgia back in 2008.
Then, of course, the Georgian military did the Russians the favour of moving first into the separatist enclave of South Ossetia sparking a furious Russian response.
But comparisons can be misleading.
Georgia was a small country that had deeply irritated Moscow and one that could do little to respond against Russia's overwhelming military might.
Many experts believe a similar full-scale Russian intervention of Ukraine is unlikely.
Given the size of Ukraine and the divisions within its population, it would simply saddle Russia with involvement in what might rapidly become a bitter civil war.
Russian pressure at the moment serves a different goal.
Ukraine is heading towards bankruptcy. It needs outside funding. Moscow knows that Western financial institutions must play some kind of role.
Its concern is to underline in as clear terms as possible that any future Ukrainian government should tilt as much towards Moscow as it does to the EU.
Russia's bottom line is that Kiev should resist any temptation to draw towards Nato.
Crimea though is another matter. For a start the Russian military does not need to invade - it is already there, leasing facilities from the Ukrainian authorities.
The bulk of Russia's Black Sea Fleet is based in Crimea with its headquarters in Sevastopol.
Russian naval personnel come and go in Sevastopol as if it were a Russian city. The navy dominates the town.
While largely made up of naval personnel, the Black Sea Fleet also has a contingent of marines and there have been a series of reports suggesting that Russian forces in and around Sevastopol have been bolstered in recent days.
Crimea has a very large pro-Russian population, who are probably in the majority.
Many Russian naval personnel have retired there - and it is distanced physically and politically from Kiev.
Russian pressure in Crimea again serves Moscow's wider purpose of reminding Ukraine's new rulers that Moscow's concerns must be considered in any future economic and diplomatic arrangements.
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Armed men patrol outside the Simferopol International Airport in Ukraine's Crimea region on Friday, February 28. The gunmen, whom Ukrainian Interior Minister Arsen Avakov called part of an "armed invasion" by Russian forces, appeared around the airport without identifying themselves. Crimea is an autonomous republic of Ukraine with an ethnic Russian majority. It's the last large bastion of opposition to Ukraine's new political leadership after President Viktor Yanukovych's ouster.
Russian troops block a road February 28 toward the military airport in Sevastopol, Ukraine, on the Black Sea coast. The Russian Black Sea Fleet is based at the port city of Sevastopol. Ukraine suspects Russia of fomenting tension in the autonomous region of Crimea, which might escalate into a bid for separation by its Russian majority.
Armed men stand guard in front of a building near the Simferopol airport on February 28. Simferopol is the regional capital of Ukraine's Crimea.
An armed man wearing no identifying military insignia patrols outside Simferopol International Airport on February 28.
Police stand guard outside the Crimea regional parliament building in Simferopol on Thursday, February 27. Armed men seized the regional government administration building and parliament in Crimea.
Police intervene as Russian supporters gather in front of the parliament building in Simferopol on February 27.
A man adds fuel to a fire at a barricade on Kiev's Independence Square on February 27. Dozens of people were killed last week during clashes between security forces and protesters.
Pro-Russia demonstrators wave Russian and Crimean flags in front of a local government building in Simferopol on February 27.
Barricades in front of a government building in Simferopol on February 27 hold a banner that reads: "Crimea Russia." There's a broad divide between those who support the pro-Western developments in Kiev and those who back Russia's continued influence in Crimea and across Ukraine.
</br>" border="0" height="360" id="articleGalleryPhoto0010" width="640">Protesters stand in front of a government building in Simferopol on February 27. Tensions have simmered in the Crimea region since the Ukraine president's ouster. 
Protesters in support of the president's ouster rally in Kiev's Independence Square, which has been the center of opposition, on Wednesday, February 26.
Security forces stand guard during clashes between opposing sides in front of Crimea's parliament building in Simferopol on February 26.
Pro-Russian demonstrators, right, clash with anti-Russian protesters in front of a government building in Simferopol on February 26.
A police officer gets pulled into a crowd of Crimean Tatars in Simferopol on February 26. The Tatars, an ethnic minority group deported during the Stalin era, is rallying in support of Ukraine's interim government.
A man places flowers at a barricade near Kiev's Independence Square on February 26.
A woman holds a photograph of a protester killed during the height of tensions on February 26 in Kiev.
Police guard a government building in Donetsk in eastern Ukraine on February 26.
Protesters remove a fence that surrounds Ukraine's parliament in Kiev on February 26.
People sing the Ukrainian national anthem at Kiev's Independence Square on Monday, February 24.
Gas masks used by protesters sit next to a barricade in Independence Square on February 24.
A woman cries February 24 near a memorial for the people killed in Kiev.
People wave a large Ukrainian flag in Independence Square on Sunday, February 23.
Two pro-government supporters are made to pray February 23 in front of a shrine to dead anti-government protesters.
A man and his daughter lay flowers at a memorial for protesters killed in Independence Square.
Former Prime Minister Yulia Tymoshenko speaks at Independence Square on Saturday, February 22, hours after being released from prison. Tymoshenko, considered a hero of a 2004 revolution against Yanukovych, was released after 2½ years behind bars.
Tymoshenko is greeted by supporters shortly after being freed from prison in Kharkiv on February 22.
A protester guards the entrance to Yanukovych's abandoned residence outside Kiev on February 22.
Anti-government protesters guard the streets next to the presidential offices in Kiev on February 22.
Anti-government protesters drive a military vehicle in Independence Square on February 22. Many protesters said they wouldn't leave the square until Yanukovych resigned.
Ukrainian lawmakers argue during a session of Parliament on Friday, February 21.
Men in Kiev carry a casket containing the body of a protester killed in clashes with police.
Protesters cheer after news of an agreement between the opposing sides in Kiev on February 21.
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