Vladimir Putin's ordered Russia's nuclear deterrent forces to be put on high alert.
The president's blaming what he's described as 'aggressive statements' by NATO leaders and economic sanctions against Moscow.
Speaking on state television earlier, he called the strict measures imposed on his country 'illegitimate'.
Meanwhile, the Ukrainian president's office says his country will hold talks with Russia, following Moscow's invasion.
They'll take place on its border with Belarus - it's not yet known when they'll be held.
Ukrainian officials have claimed 'complete control' over the country's second largest city, Kharkiv , after clashing with Russian forces.
Sky's Deborah Haynes, who's in Kiev, says there seems to have been a bit of a concession on the Russian side, given the change in location for the talks.