Russia warned the United States on Tuesday that putting conventional warheads on long-range missiles would jeopardize President Barack Obama's vision of a world free of nuclear weapons.
Two days before Obama is to sign a landmark nuclear arms reduction pact with President Dmitry Medvedev, Foreign Minister Sergei Lavrov also repeated Moscow's threat to withdraw from the treaty if U.S. missile defense plans threatened Russia.
But he suggested the plans were unlikely to pose a threat in the near future.
Lavrov was drawing lines in the sand before the two presidents sign a treaty in Prague on Thursday committing the former Cold War foes to cut their arsenals of deployed nuclear warheads by about 30 percent.
U.S. Secretary of State Hillary Clinton told reporters in Washington she was not aware of Lavrov's comments "but it's no surprise that the Russians remain concerned about our missile defense program.
"The START treaty is not about missile defense," she said.
Lavrov said Russia shared the goal of a world without nuclear arms, which Obama set out in Prague a year ago, but made clear Moscow wanted assurances that it would not end up at a strategic disadvantage.
"We believe the ultimate goal of a world without nuclear weapons is very important," Lavrov told a news conference. "But it's clear that it is impossible to move toward that goal in a vacuum."
Among potential obstacles to realizing that vision, he said, would be the emergence of space-based weapons and strategic missiles, such as the ICBMs, fitted with conventional warheads.
"To move toward a nuclear-free world, it is necessary to resolve the question of non-nuclear-equipped strategic offensive weapons and strategic weapons in general, which are being worked on by the United States, among others," Lavrov said.
Obama has acknowledged that the goal of a world without nuclear weapons may not be reached in his lifetime.
But his administration has indicated it hopes further reductions will follow once the treaty to be signed on Thursday, a successor to the 1991 START I pact, is ratified by lawmakers.
Lavrov spoke hours before Obama was to unveil a new policy calling for reduced U.S. reliance on its nuclear deterrent.
The Russian minister also said Moscow would consider withdrawing from the START successor pact if U.S. plans for a missile shield threatened to compromise its security by weakening its nuclear deterrent.
But he said the U.S. plans did not pose a threat in their initial stages.
Obama improved relations with Russia and set the stage for agreement on the START successor pact by dropping Bush-era plans for missile defense installations in Poland and the Czech Republic, which the Kremlin bitterly opposed.
The United States says the shield would be aimed to defend against nations such as Iran and is no threat to Russia.
Clinton said the United States would keep working with Russia "to try to find common ground around missile defense, which we are committed to pursuing."
