By Gordon Corera
Security correspondent, BBC News
US President Barack Obama has recommitted his administration to the goal of a world without nuclear weapons.
The move came in a written statement to a conference in Paris, as the US and international community prepare for an important six months for dealing with the spread of nuclear weapons.
President Obama has set nuclear non-proliferation as a key policy
President Dmitry Medvedev of Russia also offered a written message of support to the Global Zero conference.
The next few months are likely to be crucial in terms of nuclear disarmament issues.
The US and Russia are believed to be close to finalising a new treaty to replace Start - a nuclear treaty which expired last year. This is expected to include a significant reduction in their arsenals of strategic nuclear weapons.
It is thought that the negotiations have made significant progress in the last few weeks with only a few hurdles left, and those involved are hoping for an announcement in the coming weeks.
The Russian president in his statement to the conference said he wanted "a meaningful and viable document which will give an additional impetus to the disarmament process".
In a separate development, the Swedish and Polish foreign ministers also called on the United States and Russia to reduce their arsenals of smaller "tactical" nuclear weapons in Europe.
Sweden's Carl Bildt and Poland's Radek Sikorski made the call in the International Herald Tribune newspaper.
In April, there will be a nuclear security summit in Washington with the goal of securing vulnerable nuclear materials in four years to prevent them falling into the hands of terrorists.
In May, the Nuclear Non-Proliferation Treaty undergoes one of its five-yearly reviews.
The treaty is the main legal instrument that underpins attempts to prevent the spread of nuclear weapons.
It offers non-nuclear states help with civilian programmes in return for not developing weapons while nuclear states are supposed to negotiate in good faith to disarm.
But the 2005 review was a failure, and most of the parties feel the deal has not been functioning effectively.
The challenge of Iran's nuclear programme - which the US and others believe is masking a weapons programme - is also placing the treaty under additional pressure.
The Obama administration is also pushing for the ratification of the Comprehensive Test Ban Treaty and for negotiation of a Fissile Material Cut-off Treaty.
And it is undertaking a nuclear posture review in which the role and number of nuclear weapons is likely to be diminished.
In his statement, President Obama cautioned against fixed deadlines for disarmament which a number of governments, including the UK, are wary of.
He also warned that progress "will be neither quick nor easy", but said that a world without nuclear weapons remained one of his highest priorities.