Speaking after meeting with leaders of the 26-nation military alliance at a NATO-Russia Council on the sidelines of a NATO summit in Bucharest, Putin said, "The appearance on our borders of a powerful military bloc... will be considered by Russia as a direct threat to our country's security."
NATO members decided on Thursday to postpone offering Georgia and Ukraine the chance to join the alliance's Membership Action Plan (MAP), but promised to review the decision in December. The ex-Soviet republics had received strong U.S. backing for their bids.
President Putin had earlier threatened to retarget Russian nuclear missiles at Ukraine should Kiev join NATO, and France and Germany subsequently expressed concerns that offering Georgia and Ukraine the chance to take a key step towards membership of the alliance would unnecessarily provoke Moscow.
The former Soviet Baltic states of Latvia, Lithuania, and Estonia, all which border Russia, are currently members of NATO.
However, Putin dismissed suggestions that a new Cold War could break out, saying that there were no more ideological divides in Europe.
"No, this is impossible. No global players, Europe, the United States and Russia, are interested in returning to the past. This is unnecessary," he said.
In a bid to make up for his recent confrontational rhetoric, Putin highlighted some positive aspects of cooperation with the Western bloc, including Russia's consent at Friday's talks to transit NATO non-military supplies to the alliance's troops engaged in anti-terrorism operations in Afghanistan.
Putin said Friday's discussions had been "constructive," and called for closer ties with NATO to tackle differences that include an amended Cold War-era Conventional Forces in Europe (CFE) treaty and Washington's missile defense plans for Europe. The issues have plunged Russia's relations with the West to a post-Cold War low.
"We talked in an open and constructive way. We did not 'ping-pong' mutual accusations at each other," he said. "It was an open, businesslike and useful discussion."
On the CFE treaty, Putin said that Moscow's position had been taken into account by NATO.
Russia temporarily withdrew from the old version of the crucial arms control treaty in December over NATO countries' reluctance to ratify the document.
"My impression is that I was heard by our partners on the CFE problem. They are prepared either to ratify the existing treaty or discuss new arrangements. In any event, we have to do something together rather than taking unilateral steps ... such an approach has no future," he said.
He also dismissed the alliance's demands that Russia withdraw its troops from Moldova's breakaway region of Transdnestr as a condition for their ratification of the treaty. Putin said Moscow had fulfilled its obligations toward the former Soviet republic by pulling out heavy weaponry from the region.
"Let's be friends, guys, and discuss things honestly," he said.
Putin also said he was happy that Russia's concerns over U.S. plans to deploy a missile base in Poland and a radar in the Czech Republic had also been heard by NATO, and that Washington and Moscow would continue to discuss the issue.
"A positive moment in today's dialogue was that our national security concerns over the possible introduction of the missile shield proposed by our American partners were finally heard," he said.
Moscow had angrily rejected U.S. assurances that the missile shield elements were protection against Iran and other 'rogue' states. It somewhat softened its stance after Washington moved to ease its concerns by suggesting that Russia could have access to the bases, but has not dropped its opposition completely.
Putin added he would continue to discuss the issue over the weekend with U.S. President George Bush in Russia's Black Sea resort city of Sochi. The meeting - whose agenda will also include a broader strategic security deal between the two countries - is set to be the last between the two leaders, who are due to step down in May and January 2009, respectively.
NATO chief Jaap de Hoop Scheffer said there were no major breakthroughs at the NATO-Russia Council session, but called the meeting "frank and open."