LONDON  - Four former British foreign and defence secretaries called Monday for nuclear powers around the world to increase diplomatic efforts to eventually rid the world of nuclear weapons. Writing in The Times, Sir Malcolm Rifkind, Lord Douglas Hurd, Lord David Owen and Lord George Robertson said there "is a powerful case for a dramatic reduction in the stockpile of nuclear weapons." They noted that they were not calling for unilateral nuclear disarmament, writing that instead, the plan would only succeed "by working collectively and through multilateral institutions." The four wrote that because the world's nuclear stockpiles were mostly controlled by the United States and Russia, "if serious progress is to be made it must begin with these two countries." They encouraged the two countries to work within and extend the 1991 Strategic Arms Reduction Treaty, and called for greater transparency and use of specialists to find and secure nuclear stockpiles that lie unaccounted for. According to the authors, the Non-Proliferation Treaty is also "in need of an overhaul", and the Comprehensive Test Ban Treaty had to be brought into effect by ensuring that nine other countries " India, Pakistan, Egypt, Iran, China, Indonesia, Israel, North Korea and the United States " ratified it. "Substantial progress towards a dramatic reduction in the world's nuclear weapons is possible," they wrote. "The ultimate aspiration should be to have a world free of nuclear weapons. It will take time, but with political will and improvements in monitoring, the goal is achievable. "We must act before it is too late." Robertson was defence secretary from 1997 to 1999, and also served as NATO secretary general from 1999 to 2003. Hurd, meanwhile, was foreign secretary from 1989 to 1995, and Rifkind succeeded him and held the post until 1997. Owen was foreign secretary from 1977 to 1979.