The new U.S.-Russian arms control treaty is a much better deal for Russia than its predecessor, but Moscow reserves the right to withdraw from it if a planned U.S. missile defense system grows into a threat, Russia's foreign minister said Tuesday, AP reported. Sergey Lavrov said Russia will issue a statement outlining the terms for such a withdrawal after President Barack Obama and Russian President Dmitry Medvedev sign the treaty Thursday in Prague. The new accord replaces the 1991 Strategic Arms Reduction Treaty, or START I, which expired in December. Lavrov has said before that Russia could withdraw from the treaty. But his comments at a briefing Tuesday were his most specific yet on how and why a withdrawal could occur. «Russia will have the right to opt out of the treaty if ... the U.S. strategic missile defense begins to significantly affect the efficiency of Russian strategic nuclear forces,» he said. Moscow welcomed Obama's decision to scrap the previous administration's plans for missile defense sites in Poland and the Czech Republic, but expressed concern about plans for a revamped shield, including a possible facility in Romania. Lavrov said the site in Romania poses no immediate threat, but Russia could opt out of the new treaty if U.S. missile interceptors become capable of intercepting Russia's strategic missiles. «We have noted that the U.S. system won't have a strategic capacity in its early stages,» he said. «We shall see what will happen next. When and if this system gets a strategic capacity, we shall see whether it creates risks for our strategic nuclear forces.» The talks on a START successor had dragged on for nearly a year. They were stymied most recently by Russia's demand for an explicit link between strategic arms cuts and development of the U.S. missile defense system. The U.S. Senate, however, has opposed any restrictions on the shield. Moscow eventually agreed to have just a general statement noting a link between strategic offensive and defensive weapons. U.S. officials said the wording imposes no constraints on missile defense. Lavrov said the new agreement will be the first arms-control treaty to make the parties fully equal. He said Russia shares Obama's goal of a nuclear-free world, but said other nations must join the disarmament process, as well. -- SPA