Russia will take steps to ensure its security if Washington rebuffs its offer of co-operation on missile defence, local media quoted First Deputy Prime Minister Sergei Ivanov as saying today.
"If our proposals are not accepted - and I cannot rule that out - Russia will continue to persistently and patiently explain its position on this issue," Itar-Tass news agency quoted Mr Ivanov as saying.
"But at the same time, we will take adequate measures to ensure security, we are already taking these measures, an asymmetrical and effective response has been found."
Mr Ivanov did not say what that response involved.
At a meeting with US President George W Bush this week, Russian President Vladimir Putin proposed an expanded plan for missile defence co-operation that would involve Russia and Nato sharing data about missile launches from "rogue states".
Mr Putin said his proposal would remove the need for the United States to proceed with its plan to locate elements of a planned missile shield in Poland and the Czech Republic.
Washington says the shield is needed to protect from possible missile attacks from states such as North Korea and Iran. Moscow has argued the shield is a threat to its own national security.
Mr Bush said he would study the Russian proposals, calling them "very innovative".
But he insisted the anti-missile system must still be based in eastern Europe.
Mr Ivanov is in overall charge of Russia's defence sector and many analysts believe he one of the leading candidates to become the country's next president.