New York  - UN Secretary General Ban Ki-moon said Friday that US-Russian leadership is vital to implement treaties banning the proliferation of nuclear weapons.

US President Barack Obama and his Russian counterpart Dmitri Medvedev agreed during their meeting in London Wednesday to commit to draw up a new deal on nuclear disarmament to replace the US- Russian strategic weapons reduction programme (START) which expires at the end of 2009.

"The secretary general believes that their leadership is vital to the process leading to the achievement of a nuclear-free world," said a statement from Ban.

Ban also welcomed Obama's statement that the US would ratify the Comprehensive Nuclear Test Ban Treaty (CTBT) dealing with nuclear ballistic missiles. dpa