President Vladimir Putin on Tuesday warned that Moscow would not remain indifferent to NATO's muscle-flexing and said Russia's nuclear forces would be ready for an adequate response to any aggressor.

Putin, speaking to top generals less than two weeks before December 2 parliamentary elections, said the NATO military alliance had built up its forces close to Russia's borders.

We see that military resources of certain states and members of the NATO alliance are being built up right by our borders and in contravention of previously reached agreements, Putin said in remarks shown on state television.

We cannot allow ourselves to remain indifferent to the obvious 'muscle-flexing', Putin said.

He said strategic nuclear forces -- which control Russia's long-range nuclear missiles -- should be ready to deliver a swift and adequate response to any aggressor.

Putin, who has hiked military spending substantially over the past eight years, has sought to boost Russia's international clout after the chaos following the fall of the Soviet Union.

Talking tough about Russia's military is immensely popular locally. Polls show it strikes a chord with millions of Russians who crave for the Soviet Union's once mighty military and superpower status.

NATO is viewed with great suspicion in Russia, where Kremlin officials say expansion eastwards into the Baltic states and Central Europe shows the alliance is being used by the United States to threaten Russian interests.

KREMLIN TALKING TOUGH

Putin, who served as a KGB lieutenant-colonel in the Cold War, says he is friends with U.S. President George W. Bush. But he has berated the United States for seeking to impose its will on the world and sowing havoc with unilateralist policies, such as the war in Iraq.

Moscow and Washington have clashed over U.S. plans for a missile defense shield in Europe, differing views of Russian democracy, the future of the Serb province of Kosovo and the war in Iraq, though on Iran there has been some cooperation.

Putin said Russia's suspension of the Conventional Forces in Europe Treaty, a key arms treaty limiting forces in Europe, was one way to counter NATO's muscle-flexing.

We are not going to fulfill anything unilaterally -- our partners did not ratify the treaty and some did not even sign it, Putin said, adding sarcastically: It was a nice affair.

Russian generals say the issue of flank limits, which restrict Moscow's ability to deploy heavy armor on parts of its own territory, must be solved if Russia is to return to the treaty.

Russian proposals to set up a single missile defense system under joint control have not had an answer from the West, Putin said.

He praised the military potential of the Shanghai Cooperation Organisation (SCO), a regional grouping of Russia, China and four Central Asian states which held joint military exercises in August in Chebarkul in the Urals.

The growing defense potential of the SCO was shown in practice at the Chebarkul range, Putin said.

At the August exercises, Putin said security threats had forced Russia to resume regular airborne bomber patrols across the world, bringing back memories of the Cold War.

Putin has been keen to show off his close ties with the military, visiting a nuclear submarine, flying a bomber and calling for better wages for soldiers.

(Reporting by Dmitry Solovyov; writing by Guy Faulconbridge; editing by Caroline Drees)

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