Washington has earlier announced plans to deploy elements of its global anti-missile shield in Central Europe to shoot down ballistic missiles that could be launched by the so-called "rogue regimes," including Iran and North Korea.
"Just because now we have systems deployed potentially in the Czech Republic as well as in Poland, that does not mean that through other avenues of cooperation the [missile shield] architecture might change and evolve over time," U.S. Department of State Spokesman Sean McCormack said at a Daily Press Briefing.
"Now we are working with a variety of different countries on this," he said. "This is a global effort."
In January, the United States asked Poland and the Czech Republic, ex-Soviet allies
in Central Europe and now members of the European Union and NATO, to host elements of the missile defense system.
Washington plans to build a radar installation in the Czech Republic and a missile interceptor base in Poland in the next five years.
Poland formally agreed on Friday to start detailed negotiations with the U.S. on the deployment of parts of the missile shield on its territory.
"The Polish government expresses the intention to begin negotiations on this issue," Foreign Ministry spokesperson Andrzej Sados said, adding that any future agreement should be aimed at strengthening U.S, Polish and global security.
According to some reports, negotiations between the U.S. and Poland could start as early as the next month and if they are successful, the construction of the missile interceptor base could be completed in 3-4 years.
But the Polish government said any future missile base deal with the U.S. has to be ratified by parliament before any concrete actions are taken.
Moscow strongly opposes the deployment of a missile shield in its former backyard in Central Europe, describing the plans as a threat to Russian national security.
Russia's top military officials earlier issued strong warnings to the U.S. regarding its plans to deploy elements of its anti-missile defense system in Europe.
The chief of the General Staff of the Russian Armed Forces, Yury Baluyevsky, said in an interview with the Rossiiskaya Gazeta daily that the unilateral U.S. actions could damage the balance of power in Europe and undermine Russia's nuclear deterrence potential.
"Knowing the potential technical characteristics of fire support and weapons systems, we can confirm that despite numerous assurances that these systems are not targeted at Russia, they could still affect our deterrence capability under certain circumstances," the general said.
Baluyevsky reiterated that Russia is strictly adhering to its nuclear disarmament obligations while the U.S. is driving to base missile shield elements in Europe, which coincides with NATO expansion closer to Russian borders.
The Russian military chief earlier said that in response to the U.S. missile deployment plans, Moscow might pull out of the Intermediate-Range Nuclear Forces Treaty (INF) which eliminated nuclear and conventional ground-launched ballistic and cruise missiles with ranges of 500 to 5,500 kilometers (300 to 3,400 miles).
Following his remarks, Gen. Nikolai Solovtsov, commander of Russia's Strategic Missile Forces, said the SMF would be able to track elements of the U.S. missile defense system if deployed in Central Europe.
"If the governments of Poland and the Czech Republic make such a decision, the Strategic Missile Forces will be able to target these systems," he said.
He also said Russia possessed the technology and the capability to resume production of intermediate- and short-range missiles in the near future.