UNITED NATIONS — President Medvedev of Russia is threatening a military response to the deployment of an American missile defense system in Poland, which was once within the Kremlin’s zone of control.

Mr. Medvedev, who yesterday recognized the independence claims of two separatist Georgian provinces, told the Russian news agency RIA Novosti that, though Russia is not seeking a resumption of the Cold War, it is “not afraid” of such an outcome.

President Bush condemned Mr. Medvedev’s decision to recognize South Ossetia and Abkhazia as independent states, and Western diplomats and politicians said Russia was risking international isolation and other consequences. However, while Mr. Medvedev is warning of a possible military response to America’s missile defense system, Western and Georgian officials said they are searching for diplomatic means to answer Russia’s aggression in the Caucasus region.

Even as Russian officials yesterday invoked a Soviet-era law as the legal basis for recognizing the two regions’ independence, they dismissed as no longer relevant the U.N. Security Council resolutions that confirm the regions’ status as part of Georgian territory.

Russia also accused America of supporting Georgia beyond diplomacy and humanitarian assistance. “What the Americans call humanitarian cargoes — of course, they are bringing in weapons,” Mr. Medvedev told the BBC, referring to the arrival of a U.S. Navy destroyer, the USS McFaul, at the Black Sea port of Poti.

A deputy White House press secretary, Tony Fratto, said the ship contained “purely humanitarian aid shipments” and “nothing else.”

To underline the importance of the war in the Caucasus for America, Mr. Bush is dispatching Vice President Cheney on a trip to Georgia, Azerbaijan, and Ukraine early next month. Senator McCain’s wife, Cindy, is visiting Georgia, and his presumed Democratic rival for the presidency, Senator Obama, said in a statement that America should “further isolate Russia internationally because of its actions.”

“At a time of high energy prices and instability in global markets, it is important to understand that events in Georgia, part of a strategic energy corridor, affect individual lives far beyond the Caucasus,” Mr. McCain said in a statement.

If the Baku-Tbilisi-Ceyhan oil pipeline, which supplies Europe, “were destroyed or controlled by Russia, global energy supplies would be even more vulnerable to Moscow’s influence, with serious consequences on the world energy market,” he added.

European leaders announced yesterday that they would convene a summit on the crisis next week. The European Union strongly condemned Russia’s decision to recognize the two regions’ independence, which is “contrary to the principles of Georgia’s independence, sovereignty and territorial integrity,” France, which is serving as E.U. president, said.

The decision to recognize the independence of the two breakaway regions “exacerbates tensions and complicates diplomatic negotiations,” Mr. Bush said in a statement released by the White House. “In accordance with United Nations Security Council Resolutions that remain in force, Abkhazia and South Ossetia are within the internationally recognized borders of Georgia, and they must remain so.”

In response, the Russian ambassador to the United Nations, Vitaly Churkin, said actions by President Saakashvili of Georgia in effect voided the Security Council provision relating to the country’s territorial integrity. Georgia’s aggression “dashed all these previous resolutions,” Mr. Churkin told The New York Sun at a press conference.

At the same time, “the law of the USSR” entitled “autonomous entities” to secede from Soviet republics such as Georgia, the Russian Foreign Ministry said in a statement yesterday, adding that Georgia “prevented Abkhazia and South Ossetia from exercising that right.”

“There is no way you can dash, or cancel, or terminate a Security Council resolution by force,” a French U.N. ambassador, Jean-Pierre Lacroix, told the Sun. “The only body that is able to change a resolution of the Security Council is the Security Council itself.” He acknowledged, however, that after yesterday’s “dramatic change,” there is a little the council can do, and he characterized the Kremlin announcement as a “far-reaching decision that will have wide-ranging implications, I think even beyond the Georgia situation.”

Russia moved a large number of troops and tanks into Georgian territory on August 8, after Georgian forces shelled South Ossetian positions held by Russian-backed separatists. Russia now controls a major highway that cuts across Georgia, as well as the country’s main port, Poti. It also is refusing to negotiate with Mr. Saakashvili, and the Russian Foreign Ministry expressed in its statement yesterday the hope that the Georgian people “will eventually find worthy leaders” to replace him.

Mr. Churkin said he also hoped that more countries would extend diplomatic recognition to the breakaway regions, and that “eventually” the two new countries would become members of the U.N. General Assembly.