The US has signed the test ban treaty but has not ratified it. Obama pledged to bring the US up to date with that treaty.

UN Secretary General Ban Ki-moon praised the US and Russia for leading nuclear disarmament by example.

'Nuclear disarmament is the only sane path to a safer world,' he said.

'I urge the Security Council to make the most of this moment,' he told the council meeting filled with celebrities, including former US secretary of state Henry Kissinger and actor Michael Douglas, who is a UN messenger of peace on disarmament.

'It should not be a one-time event,' Ban said. 'We must sustain the momentum.'

In addition to Obama, Presidents Hu Jintao of China, Nicholas Sarkozy of France and Dmitri Medvedev of Russia and British Prime Minister Gordon Brown were scheduled to attend. Those five countries are permanent members with veto power in the 15-nation Security Council.

The 10 council members elected for two-year terms were also represented by their presidents and prime ministers. They included Japanese Prime Minister Yukio Hatoyama, Libyan leader Muammer Gaddafi, Ugandan President Yoweri Museveni, Mexican President Felipe Calderon, Vietnamese President Nguyen Minh Triet and Turkish Prime Minister Recep Tayyip Erdogan.