The United States has criticised what it calls "bellicose rhetoric" from Russia over US plans to develop a missile shield in Europe.
Russia said it would be forced to react with military means if the US went ahead with its plan for a shield based partly in the Czech Republic.
The reaction was "designed to make Europeans nervous about participating" said a Pentagon spokesman.
A White House spokesman said dialogue with Russia would continue.
"We seek strategic cooperation on preventing missiles from rogue nations, like Iran, from threatening our friends and allies," said White House spokesman Gordon Johndroe.
He said the US and Russia should be "equal partners".
Moscow says siting the system near its borders could weaken its own defences, despite US assurances that it is designed to counter a threat from the Middle East, not from Russia.
It has previously threatened to aim its own missiles at any eventual base in Poland or the Czech Republic.
A deal, signed by US Secretary of State Condoleezza Rice in Prague on Tuesday, allows a tracking radar base to be set up on Czech territory.
'Not our choice'
The Russian foreign ministry statement said: "If a US strategic anti-missile shield starts to be deployed near our borders, we will be forced to react not in a diplomatic fashion but with military-technical means."
It said there was "no doubt that the grouping of elements of the strategic US arsenal faced towards Russian territory" would mean Moscow had to "take adequate measures to compensate for the threats to its national security".
"This is not our choice," it added.
The foreign ministry said it would continue to monitor developments but would remain open to constructive talks on issues of strategic stability.
The BBC's Adam Brookes in Washington cites Russia's ambassador to the UN as suggesting that the phrase "military-technical means" does not mean military action, but more likely a change in Russia's strategic posture, perhaps by redeploying its own missiles.
More likely still, our correspondent says, is that the Russians are trying to frighten the Czech parliament into backing out of the whole deal.
The next question, he says, is whether Poland will accept missile defence facilities as well, and how the Russians will respond to that.
The plans remain unpopular in the Czech Republic, while the US has failed to reach agreement with Poland on placing other parts of the system there.
The plans involve siting the tracking radar system in the Czech Republic and 10 interceptor missiles in Poland. The US wants the sites to be in operation by about 2012.
US criticises 'bellicose' Russia
The United States has criticised what it calls "bellicose rhetoric" from Russia over US plans to develop a missile shield in Europe.
Russia said it would be forced to react with military means if the US went ahead with its plan for a shield based partly in the Czech Republic.
The reaction was "designed to make Europeans nervous about participating" said a Pentagon spokesman.
A White House spokesman said dialogue with Russia would continue.
"We seek strategic cooperation on preventing missiles from rogue nations, like Iran, from threatening our friends and allies," said White House spokesman Gordon Johndroe.
He said the US and Russia should be "equal partners".
Moscow says siting the system near its borders could weaken its own defences, despite US assurances that it is designed to counter a threat from the Middle East, not from Russia.
It has previously threatened to aim its own missiles at any eventual base in Poland or the Czech Republic.
A deal, signed by US Secretary of State Condoleezza Rice in Prague on Tuesday, allows a tracking radar base to be set up on Czech territory.
'Not our choice'
The Russian foreign ministry statement said: "If a US strategic anti-missile shield starts to be deployed near our borders, we will be forced to react not in a diplomatic fashion but with military-technical means."
It said there was "no doubt that the grouping of elements of the strategic US arsenal faced towards Russian territory" would mean Moscow had to "take adequate measures to compensate for the threats to its national security".
"This is not our choice," it added.
The foreign ministry said it would continue to monitor developments but would remain open to constructive talks on issues of strategic stability.
The BBC's Adam Brookes in Washington cites Russia's ambassador to the UN as suggesting that the phrase "military-technical means" does not mean military action, but more likely a change in Russia's strategic posture, perhaps by redeploying its own missiles.
More likely still, our correspondent says, is that the Russians are trying to frighten the Czech parliament into backing out of the whole deal.
The next question, he says, is whether Poland will accept missile defence facilities as well, and how the Russians will respond to that.
The plans remain unpopular in the Czech Republic, while the US has failed to reach agreement with Poland on placing other parts of the system there.
The plans involve siting the tracking radar system in the Czech Republic and 10 interceptor missiles in Poland. The US wants the sites to be in operation by about 2012.
