The United States signed a pact on Tuesday to build part of a U.S. missile defence shield in the Czech Republic, prompting neighbouring Russia to warn it will react with military means if the shield is deployed.
The U.S. and Czech foreign ministers toasted with champagne after signing the accord to place a tracking radar southwest of Prague as part of a system to protect against the perceived threat of missile attack from countries such as Iran.
But Russia, in a statement reminiscent of Cold War rhetoric, warned the United States against deploying the shield close to its borders.
"If the real deployment of an American strategic missile defence shield begins close to our borders, then we will be forced to react not with diplomatic methods, but with military-technical methods," the Foreign Ministry said in a statement on its www.mid.ru website.
It did not give specifics but analysts said the threat appeared aimed at stoking European opposition to the shield.
In response, the Pentagon accused Moscow of trying to make Washington's European allies nervous with its aggressive talk.
"I can only assume Russia's bellicose rhetoric is designed to make Europeans nervous about participating in this system, but that won't work," said press secretary Geoff Morrell.
Still, the White House said it would keep talking to Russia, trying to explain that the missile shield was not aimed against Moscow.
After President George W. Bush met Russian President Dmitry Medvedev on the fringes of the G8 summit, in Japan, White House spokesman Gordon Johndroe said: "We will continue to have a dialogue with the Russians on this matter as Presidents Bush and Medvedev reaffirmed this week in their meeting in Japan."
In 2007, former President Vladimir Putin, now prime minister, said Russia could aim missiles at European countries if the missile shield, which Moscow considers a threat to its national security, goes ahead.
The Pentagon insists the missile defence system is designed to counter missile threats from the Middle East, not Russia.
"We've made several very robust offers to the Russians in terms of how we could collaborate and how we are willing to have as much transparency as possible with respect to this missile defence system, what its design is and what its intent is," Pentagon spokesman Bryan Whitman told Reuters Tuesday.
Russia's Foreign Ministry said in the statement Moscow's proposals to the United States on the shield had been ignored.
