Russia has threatened to deploy missiles to target the US missile shield in Europe if the US fails to allay the country's concerns about its plans.
In a televised statement on Wednesday, Dmitry Medvedev, the Russian president, said that his country would have to take military countermeasures if the US continues to build the shield without legal guarantees that it will not be aimed against Russia.
The US plan calls for placing land- and sea-based radars and interceptors in European locations, including Romania and Poland, over the next decade and upgrading them over time.
The Obama administration has repeatedly said the shield is needed to fend off a potential threat from Iran, but Russia fears that it could erode the deterrent potential of its nuclear forces.
Medvedev still hoped for a deal with the US on missile defence, but he strongly accused the US and its NATO allies of ignoring Russia's worries.
He made it clear that Russia will not be satisfied by simple declarations and wants a binding agreement, saying: "When we propose to put in on paper in the form of precise and clear legal obligations, we hear a strong refusal."
In response to Medvedev's statement, Captain John Kirby, a US Pentagon spokesman, said: "I do think it's worth reiterating that the European missile defence system that we've been working very hard on with our allies and with Russia over the last few years is not aimed at Russia."
"It is ... designed to help deter and defeat the ballistic missile threat to Europe and to our allies from Iran."
Anders Fogh Rasmussen, the NATO secretary-general, said he was "very disappointed" with Russia's threat to deploy missiles.
He said that "would be reminiscent of the past and ... inconsistent with the strategic relations NATO and Russia have agreed they seek".
"Co-operation, not confrontation, is the way ahead," Rasmussen said in a statement.
Russia has agreed to consider a proposal NATO made last autumn to co-operate on the missile shield, but the talks have been deadlocked over how the system should be operated.
Russia has insisted that it should be run jointly, which NATO has rejected.
Medvedev also said that Moscow may opt out of the New START arms control deal with the US and halt other arms control talks, if the US proceeds with the missile shield without meeting Russia's demand.
The Americans had hoped that the START treaty would stimulate progress in further ambitious arms control efforts, but such talks have stalled because of tension over the missile plan.