Vladimir Putin, Russia's president, has said his country will take "retaliatory steps" if the US proceeds with a plannd missile system for Europe.
Such steps could mean aiming missiles at European targets and in an interview on Monday Putin also said that neither North Korea nor Iran had missiles that would be combated by the defence system.
"We are being told the anti-missile defense system is targeted against something that does not exist," Putin told foreign reporters in Moscow, saying the planned missile shield would cover Russia's territory up to the Ural Mountains.
"It would be funny if it wasn't so sad," he said.
Washington plans to place a radar system in the Czech Republic and interceptor missiles in neighbouring Poland, in an attempt, according to Washington to counter a potential threat from Iran and North Korea.
In an earlier interview, published by the Italian newspaper Corriere della Sera on Sunday, Putin suggested that Russia could respond to the threat by aiming its nuclear weapons at Europe.
"If the American nuclear potential grows in European territory, we have to give ourselves new targets in Europe," he was quoted as saying.
'An awkward dinner party'
Putin's comments come before the president joins other G8 leaders at a summit in Heiligendamm, Germany on Wednesday.
It is his last such gathering before leaving office in 2008 and some analysts believe he will again insist that Russia is not a "monster" in its relations with Europe.
"Putin won't have to shake his fists and bare his teeth. He will rather show that his country is on an equal footing with the others," Masha Lipman, an analyst from the Carnegie Moscow Centre, said.
But James Nixey, a Russia analyst at the British think tank Chatham House, said: "Relations are as bad as they've ever been ... It will be like an awkward dinner party."
A week ahead of the summit, Russia tested a new multiple warhead missile in what officials described as a response to the US plans.
Washington claims its missile defence system would guard Europe against potential missile threats from Iran or North Korea, while Moscow sees the move as military expansion into an area that in the past was influenced greatly by the Soviet Union.