The Russian president tasked his defence chiefs with increasing his country's nuclear "deterrence forces" on high alert after Western countries took "unfriendly" steps against his country.
There are already high tensions over Russia's invasion of Ukraine, and Putin's order will cause further alarm.
Moscow is home to the second-largest nuclear arsenal in the world, as well as a trove of ballistic missiles which act as a deterrent.
"I order the defence minister and the chief of the general staff of the Russian armed forces to put the deterrence forces of the Russian army into a special mode of combat service," Putin stated.
"You see that Western countries are not only unfriendly to our country in the economic sphere -- I mean illegitimate sanctions," he spoke, during a televised address. "Senior officials of leading NATO countries also allow aggressive statements against our country."
"Affirmative," replied Defence Minister Shoigu.
The Russian president's decision to invade Ukraine on Thursday sent shockwaves around the globe.
Ground forces from the north, east and south have pushed into Ukraine, but have encountered fierce resistance from Ukrainian troops, whose intensity has probably surprised Moscow, according to Western sources.
Some Russian troops are said to be demoralized and exhausted by Ukrainian authorities, claiming that dozens have surrendered.