"You can rest assured that our security will be provided under any circumstances," Deputy Foreign Minister Sergei Kislyak said.
Moscow has strongly opposed the possible deployment by the U.S. of 10 interceptor missiles in Poland and an accompanying radar in the Czech Republic as a threat to its security and international nuclear deterrence. Washington says the defenses are needed to deter a possible strike from Iran.
On Russian measures to counter the U.S. plans, Kislyak said: "We won't speculate on what measures will be used. Military specialists always have many options."
Russia earlier vowed to retaliate against the U.S. missile shield plans in Central Europe and even warned it could point nuclear missiles at countries that accept U.S. missile defense components.
Some analysts have suggested that Russia impose trade restrictions on countries that allow the placement of U.S. missile defense systems on their territory, and suspend military cooperation with NATO.
However, Kislyak said that talks with the United States over the European missile shield will continue despite Washington's recent agreement with the Czech Republic on deploying a radar in the country.
"Our dialogue with the U.S. is sufficiently strong on a broad range of strategic issues - strategic, offensive, and defensive. I am sure that this dialogue will continue," he said.
During their visit to Moscow in late March, U.S. Defense Secretary Robert Gates and Secretary of State Condoleezza Rice offered to let Russia monitor the proposed U.S. missile and radar bases in Central Europe.
Washington has also said it will not activate the "missile shield" until there is a "clear and present" threat from Iran or other potential adversaries.
Kislyak reiterated that U.S. proposals made at bilateral talks with Russia on the issue are not consistent with the actual situation.
"It is technically possible to implement what the U.S. Secretary of State proposed initially. But general political statements that we are hearing are still a far cry from what we are seeing at the talks. Obviously, our American colleagues are not ready for a serious discussion on these issues," he said.
"Without going into technical details, we do not have at present a clear understanding what lies behind general assurances from Washington that the U.S. missile shield is transparent. In what sense?" Kislyak said.
Washington had suggested that Russia negotiate directly with Poland and the Czech Republic on giving Russian officers permanent access to the planned facilities, but the talks stalled, as both Polish and Czech officials categorically refused to allow the permanent presence of Russian military personnel on their territory.
The Russian diplomat said the next "2+2" meeting between the Russian and U.S. foreign and defense ministers over the U.S. missile shield in Europe is likely to be held in 2009.
"We can work this out if both sides show their desire to do so, but at present we remain on the level of general official statements," Kislyak said.
