Russian President Vladimir Putin has warned that US plans to build a missile defence system in eastern Europe would raise the risk of "mutual destruction".
Poland and the Czech Republic are keen to allow the US to site missile bases and radars on their territory.
Mr Putin spoke a day after threatening to halt involvement with a treaty limiting conventional arms in Europe.
"The threat of causing mutual damage and even destruction increases many times," he told Russian media.
"This is not just a defence system, this is part of the US nuclear weapons system," the Itar-Tass news agency quoted him as saying after meeting Czech President Vaclav Klaus.
Hmmmm I agree with him. BBC News Report