Russia's top diplomat accused the United States of launching a new arms race as the two nations traded barbs Wednesday over US plans to erect a missile defense system in countries formally under Moscow's influence. Russian Foreign Minister Sergey Lavrov complained that the US rationale for the shield is thin and suggested that US assurances to Russia amount to a brush-off. "All they are saying is, 'Don't worry it's not aimed at you," Lavrov said. He called the plan a threat to Russia and added, "the arms race is starting again." US Secretary of State Condoleezza Rice said the United States repeatedly has explained its plan to Russia in considerable detail, and stands ready to discuss the matter further. She tartly noted that Russian President Vladimir Putin himself had said Russia's own strategic defenses could easily overpower the US system.