Russian President Vladimir Putin has repeated his threat to target missiles at neighbouring states if they site parts of the planned US missile shield.
Mr Putin said the US proposal to base interceptors in Poland and a radar in the Czech Republic "threatens our national security".
The Russian leader said earlier this week Moscow might target Ukraine if it sited elements of such a system.
The US says it is designed to block any missiles from North Korea or Iran.
But Mr Putin reiterated Russian objections to the scheme during his annual news conference at the Kremlin.
Russia's response would be to "retarget our missiles toward a system that we aren't creating", he was quoted by AP news agency as saying.
"We are warning people ahead of time: if you take this step, then we will make this step."
Russia holds presidential elections next month which are widely expected to be won by Mr Putin's chosen successor, First Deputy Prime Minister Dmitry Medvedev.
