Russian President Vladimir Putin ordered Russia's nuclear deterrent forces to be on high alert.
The move was blamed on statements from NATO and western nations.
Putin told his top advisors that the Western countries were taking hostile actions toward Russia in the economic sphere.
Senior officials of leading NATO countries make aggressive statements against our country. He ordered the Minister of Defense and the Chief of the General Staff to put the deterrent forces of the Russian army in a special regime of duty.
The Washington Post reported that the Russian president ordered the country's nuclear weapons to be prepared for the increased possibility of launch.
The Russian government warned that there would be a strong response from Moscow if any nation interfered in the affairs of Ukraine.
Russia's Foreign Affairs Ministry said on Wednesday that there should be no doubt that sanctions will receive a strong response.
The European Union and the UK followed the US in placing personal sanctions against Putin.
Russia warned it would cut ties with the US if Putin was hit with sanctions. A Kremlin spokesman said in January that such actions would be like a break in relations.
Russian forces attacked Ukraine. There is no evidence to support the claim that the Ukrainian government was committing genocide against ethnic Russians.
The invasion is to prevent the further expansion of the North Atlantic Treaty Organization.