"This agreement is consistent with the disarmament obligations by the two largest nuclear weapon states under Article VI of the Treaty on the Non-Proliferation of Nuclear Weapons (NPT)," the UN secretary general, who was on a visit to Ireland, said in a statement released by his office.

"The Secretary General believes that this agreement will make a significant contribution to the process of nuclear disarmament, as well as nuclear non-proliferation, during the lead-up to the 2010 NPT Conference and eventually to achieving the goal of a nuclear weapon-free world," added the statement by Ban's spokeswoman Michele Montas.

US President Barack Obama and his Russian counterpart Dmitry Medvedev signed a declaration in Moscow Monday pledging to reach a new nuclear arms reduction pact to replace the 1991 Strategic Arms Reduction Treaty (START). Obama said it provides for cuts of "up to a third" from current limitations.

START is due to expire on December 5 but the declaration gave no target date for a renewal, instructing negotiators to complete their work as quickly as possible.

The declaration called for a reduction in the number of nuclear warheads in Russian and US strategic arsenals to between 1,500 and 1,675 within seven years and the number of ballistic missile carriers to between 500 and 1,100.

The cuts go beyond those levels set in the 2002 Strategic Offensive Reductions Treaty (SORT), which calls for both countries to reduce the number of deployed warheads to between 1,700 and 2,200 on either side by 2012.

In May, Ban told a conference on disarmament that he was encouraged by recent remarks by the US and Russian leaders and urged the broader international community to undertake a new multilateral approach to ensure sustainable progress towards disarmament.