(CNN) -- When Russia invaded and annexed Crimea, Western leaders warned Russia against trying the same trick in mainland Ukraine. Russia is now trying the same trick in mainland Ukraine. Over the past several days, masked, heavily armed men have seized strategic locations in eastern Ukraine. In Kharkiv, pro-Russian armed forces have occupied City Hall. In Donetsk, they have taken control of the regional legislature building and the interior ministry. In Luhansk, they have taken the compound of the state security agency. In the city of Kramatorsk, in the Donetsk region, armed men shot their way into police headquarters. Cell phone towers are being toppled through the area, according to Ukraine's acting interior minister, apparently with a view to silencing nonmilitary communications.
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Gunmen seize key parts of eastern Ukraine; pro-Russian forces create instability
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David Frum: Remark that military intervention won't work implies West will look away
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Frum: Russia threatens stability of Europe; NATO observers need to monitor events
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He says sanctions must hurt Russian investments; Ukraine's weak military needs help
The @placeholder' actions in Ukraine do threaten the general peace.