Russian President Vladimir Putin ordered the country's deterrence forces to be placed on "a special mode of combat duty" in a meeting with top defense officials.
Senior officials of leading NATO members issued "aggressive statements" against Russia, Putin on Sunday said at a meeting with Defense Minister Sergei Shoigu and Chief of the General Staff of the Russian Armed Forces, Valery Gerasimov.
Putin said Western countries are imposing "illegitimate sanctions" against Russia's economy, Xinhua news agency reported.
The decision to put the deterrence forces on combat duty was made as Russia has been conducting "a special military operation" in Ukraine since early Thursday.
Russian forces had destroyed 975 Ukrainian military infrastructure objects, Russian Defense Ministry spokesman Igor Konashenkov said on Sunday morning.
Russia has blockaded several cities in eastern and southern Ukraine.