Five of the world's largest nuclear powers pledged on Monday to work together toward a world without nuclear weapons" in a rare statement of unity amid rising East-West tensions. "A nuclear war cannot be won and must never be fought," said the joint statement, which was issued simultaneously by the United States, Russia, China, the United Kingdom and France. "As nuclear use would have far-reaching consequences, we also affirm that nuclear weapons - for as long as they continue to exist - should serve defensive purposes, deter aggression, and prevent war." The statement also stressed the importance of preventing conflict between nuclear-weapon states from escalating, describing it as a "foremost responsibility." The statement released by the five powers ... as permanent members of the United Nations Security Council, called on all states to create a security environment "more conducive to progress on disarmament with the ultimate goal of a world without nuclear weapons with undiminished security for all. The five pledged to adhere to the 1970 Nuclear Nonproliferation Treaty (NPT) which obligates them "to pursue negotiations in good faith on effective measures relating to cessation of the nuclear arms race at an early date and to nuclear disarmament." Some of the text of the statement ... echoes a statement issued by the five nations after a December conference in Paris that laid the groundwork for the since delayed review of the treaty.