President Vladimir Putin cautioned Tuesday that Russia would increase the combat-readiness of its strategic nuclear forces to ensure a "swift and adequate response to any aggressor."

Putin also said that Russia's will be pulling out of a key arms control treaty, which he calls a necessary response to NATO "muscle-flexing" near its frontiers.

The statements, which come amid simmering tensions between Moscow and the West, reflect the Kremlin's assertive posture less than two weeks before Russia's Dec. 2 parliamentary elections.

"In violation of previous agreements, military resources of NATO members are being built up next to our borders. Of course, we cannot allow ourselves to remain indifferent to this obvious muscle-flexing," Putin said in televised remarks at a meeting of top military officials.

Both statements elicited a phone call from President Bush, who thanked the Russian leader for his support and encouragement of the process that is underway between the Israelis, Palestinians and the international community. The two leaders also discussed missile defense and expressed their desire to continue working together on the issue, National Security Council spokesman Gordon Johndroe told FOX News.

Russia has fiercely opposed U.S. plans to establish missile defense sites in Poland and the Czech Republic, and the deployment of U.S. and other NATO forces on the territory of former Soviet republics and satellite states in Europe.

Putin said that the suspension of Russia's obligations under the Conventional Forces in Europe (CFE) Treaty, a key pact limiting the deployment of tanks, aircraft and other heavy conventional weapons across the continent, was part of Russia's response.

Both houses of the Russian parliament have endorsed Putin's call for the suspension. Putin justified the decision, which is slated to take effect Dec. 12, by pointing to NATO nations' own failure to ratify an amended version of the treaty.

"We won't observe any obligations unilaterally," Putin said. "Our partners haven't ratified the amended version of the treaty, and some haven't even signed it. Shall we do it unilaterally for years?"

He said Russia would consider resuming its obligations under the treaty only after Western nations ratify it.

The 1990 CFE treaty, which originally set limits on weapons of NATO and Warsaw Pact countries, was revised in 1999. Russia says the old version has lost relevance since former Soviet satellites have joined NATO.

Russia ratified the updated treaty in 2004, but the United States and other NATO members have refused to follow suit, saying Moscow first must fulfill obligations to withdraw forces from Georgia and from Moldova's separatist Trans-Dniester region.

As a counterproposal to the U.S. missile defense plans, Putin earlier this year offered the United States joint use of a Soviet-built, Russian-operated radar in Azerbaijan. Washington said it was studying the proposal, but U.S. officials said the radar couldn't be considered as a replacement for the sites in Poland and the Czech Republic.

"Regrettably, Russian proposals about the creation of a joint missile defense system with equal access for all its participants have remained unanswered," Putin said Tuesday.