UN Secretary General Kofi Annan has called on world leaders to reinforce their commitment to a treaty aimed at reducing the threat from nuclear arms.
"We all bear a heavy responsibility to build an efficient, effective, and equitable system that reduces nuclear threats," he told a UN meeting.
He also called upon former Cold War rivals Russia and the US to seriously reduce their current nuclear arsenals.
Mr Annan was addressing a conference on the Nuclear Non-Proliferation Treaty.
The treaty, signed in 1970, was designed to stop the spread of weapons, achieve nuclear disarmament and promote the peaceful use of nuclear energy.