"We are against NATO's enlargement on the whole, in principle," Vladimir Putin said commenting on Ukraine and Georgia's drive to join the alliance.
Ukraine and Georgia, backed by the U.S., have long been seeking NATO membership. At a NATO summit in early April, NATO powers voted against admitting Ukraine and Georgia to the alliance's Membership Plan, the first step towards membership, but said they would review the decision at the end of the year.
Putin said that NATO was formally created to counter the alleged Soviet threat but the Soviet Union collapsed long ago and there was no need to erect new "invisible" Berlin Walls in Europe.
"There is no Soviet Union, and there is no such a threat anymore but this organization still exists," he said. "The question arises: against whom do you build friendships?"
NATO's expansion will only hamper common efforts to stave off current global threats and challenges because it creates distrust among partners, the Russian prime minister said.
Putin said Russia has every reason to worry that new NATO bases could appear close to its borders if Ukraine and Georgia join the alliance.
"We are concerned that if these countries become part of NATO today, tomorrow we will see offensive missile systems deployed on their territory which will pose a serious threat to us," Putin said also referring to U.S. plans to place elements of its missile shield in Central Europe.
The U.S. plans to place 10 interceptor missiles in Poland and a radar station in the neighboring Czech Republic.
Russia has fiercely opposed the plans, saying the Central European shield would destroy the strategic balance of forces and threaten Russia's national interests.
Washington wants to deploy its missile defense elements in Central Europe purportedly to counter a missile threat from Iran and other "rogue" states. However, Russia dismisses all statements about Iran's nuclear threat saying that Tehran has neither the military potential nor interest in attacking European countries, its major trading partners.
"As Bismark said long ago, what really counts is potentials rather than goodwill intentions or statements," Putin said. "And all we see is that military infrastructure is getting closer and closer to our borders. Why? Nobody threatens each other anymore."