“We will view any use of nuclear weapons against Russia or its allies, be it of small, medium or any force, as a nuclear attack on our country,” Putin said.
“Our response will be immediate. Nobody should have any doubts about that," he added.
Delivering his annual state of the nation speech in Moscow, Putin expressed concerns about the new US posture, which has lowered the threshold for the use of nuclear weapons.
Russian president also unveiled an array of new nuclear weapons, saying they could hit almost any point in the world and not be intercepted.
Putin made these comments weeks before an election he is expected to win.
Polls indicate Putin should be easily re-elected on March 18.
