The new Ukrainian government in Kiev is under mounting pressure to keep the country from unraveling as pro-Russian demonstrators in Kharkiv, Donetsk, Lugansk and other eastern cities occupy government buildings and demand to be reunited with Moscow. Whether or not this is prelude to a replay of Russia's lightning takeover of the Crimea last month, President Barack Obama and European leaders must make absolutely clear to Russian President Vladimir Putin that his country will pay a heavy price for any attempt to change the map of Europe again by force.

American officials say the unrest is clearly being inspired and organized by Russia, which has amassed thousands of troops along its border with Ukraine who appear poised to invade the country. There is little if anything the U.S. and its allies can or should do militarily to counter that threat, at least in the short term. But Mr. Putin should be put on notice that tough economic sanctions aimed at crippling Russia's growth will be the inevitable Western response if he launches another reckless military adventure.

Whether the Kremlin will heed that warning remains in doubt. After Russian special forces troops wrested control of Crimea from Kiev last month in a mostly bloodless coup, Mr. Putin insisted he had no further territorial ambitions in the region. But this week's carefully orchestrated protests by pro-Moscow demonstrators in Russian-speaking portions of eastern Ukraine appear to be following the same playbook that preceded Mr. Putin's seizure of Crimea.

There, as in Crimea, protesters are calling for an immediate referendum on whether to remain part of Ukraine and loudly proclaiming alleged threats to their safety from right-wing groups aligned with the government in Kiev. Similarly, Mr. Putin has warned that Russia will intervene to protect the rights of Ukraine's Russian-speaking minority if the situation worsens, which it is likely to do, especially if Russian operatives are indeed working behind the scenes to foment outbreaks of violence.

That's why Ukrainian officials have every reason to be alarmed by the prospect that the Kremlin may not be satisfied until their country is effectively dismembered and its government crushed. At the same time they have to be careful not to do anything that would give Mr. Putin an excuse to send troops across the border. On Tuesday, Ukrainian police removed pro-Russian demonstrators who had occupied a building in Kharkiv, apparently without bloodshed. But protesters who sized a regional administrative center in the city of Donetsk are still there and have vowed not to leave the building until their demands are met. That poses a tricky problem for authorities who want to get them out without using force.

Meanwhile, the most dangerous situation appears to be in the city of Lugansk, where police reported demonstrators had seized the security agency headquarters and are holding 60 hostages at gunpoint. It's unclear exactly who the hostages are or how long the demonstrators intend to hold them (more recent reports suggest that at least some of them have been released). But in the current volatile situation it's all too easy to imagine a provocation from one side or the other that results in people being killed — and provides Moscow with a convenient excuse for sending in troops.

Everything that has happened so far suggests that the crisis in Ukraine may not be the spontaneous upheaval it first appeared to be but rather that it was the result of careful planning by the Kremlin aimed at restoring Russia's sphere of influence in the republics of the former Soviet Union and fulfilling Mr. Putin's dreams of empire in Eastern Europe. If that's true, the fact that it apparently caught the West by surprise represents an astonishing intelligence failure by the U.S. and its allies.

Nor may It be a coincidence that both the annexation of Crimea last month and the 2007 dismemberment of Georgia both occurred in the aftermath of Olympic Games that may have momentarily distracted the world's attention from what was brewing. Mr. Putin ultimately paid no price for flouting international norms in Georgia, and he probably expects this time will be no different. It's up to Mr. Obama and Western Europe's leaders together now to convince him otherwise, and they must do so in no uncertain terms.


To respond to this editorial, send an email to talkback@baltimoresun.com. Please include your name and contact information.