"Although we averted a nuclear nightmare during the Cold War, we now face proliferation of a scope and complexity that demands new strategies and new approaches," Obama told the talks which included outgoing UN nuclear watchdog chief Mohamed ElBaradei.

"Just one nuclear weapon exploded in a city, be it New York or Moscow, Tokyo or Beijing, London or Paris, could kill hundreds of thousands of people."

The summit came as Iran’s suspect atomic program has once again been thrust into the spotlight, with world powers warning more sanctions could follow if Tehran refuses to comply with UN demands to rein in its nuclear ambitions.

The Iranian mission at the United Nations Thursday hit out at fresh allegations that it was seeking to develop nuclear arms, saying they were "totally untrue."

The Security Council resolution, adopted unanimously, commits member nations to work toward a world without nuclear weapons and endorses a broad framework of actions to reduce global nuclear dangers.

Quoting former US president Ronald Reagan, Obama told the meeting that "a nuclear war cannot be won and must never be fought."

Obama became the first American president to chair a meeting of the UN Security Council as the United States holds the rotating presidency of the 15-member body this month.

"We must never stop until we see the day when nuclear arms have been banished from the face of the earth. That is our task. That can be our destiny," Obama said.

US officials have stressed the aim of the summit, which was shunned by Libyan leader Moamer Kadhafi, was to reinvigorate the nuclear Non-Proliferation Treaty (NPT), which will be the subject of a key review conference next year.

Chinese President Hu Jintao said countries with the largest nuclear arsenals — the United States and Russia — "should continue to take the lead in making drastic and substantive reductions in their nuclear weapons."

And he proposed that all nuclear weapon states "abandon the nuclear deterrence policy based on first use of nuclear weapons and take credible steps to reduce the threat of nuclear weapons.

His Russian counterpart Dmitry Medvedev said one of the major security threats was the danger that nuclear components will end up "in the hands of terrorists." He called for ways to make sure that would not happen.

Medvedev added Moscow was ready to "move further" to reduce its nuclear arsenal.

The United States and Russia are seeking to agree on a successor to the landmark 1991 Strategic Arms Reduction Treaty (START) before it expires on December 5.

The Security Council meeting comes as Iran’s President Mahmoud Ahmadinejad has offered landmark talks between Iranian and US experts for the first time to allay fears about his country’s nuclear program.

"Why not just let them sit and talk and see what kind of capacity they can build? I think it is a good thing to happen," Ahmadinejad said in an interview with the Washington Post and Newsweek.

And he said Iran would offer to purchase enriched uranium for medical purposes from the United States at upcoming talks with six world powers on October 1 in Geneva.

Russia on Wednesday signalled it could back sanctions if Tehran fails to make concessions at the October 1 meeting with the five permanent members of the UN Security Council — which are all declared nuclear powers — plus Germany.

The council resolution also urges all states to comply with the obligations of the NPT, to refrain from conducting nuclear test explosions and ratify the Comprehensive Test Ban Treaty (CTBT).

The CTBT, which bans any nuclear blasts for military or civilian purposes, was signed in 1996 by 71 states, including the five main nuclear powers, and now has 181 member states.

Japan’s Prime Minister Yukio Hatoyama meanwhile urged all world leaders to visit the atom-bombed Japanese cities of Hiroshima and Nagasaki to "absorb with their own eyes and ears the cruelty of nuclear weapons."

The annual UN General Assembly was meanwhile to be addressed later Thursday by Israeli leader Benjamin Netanyahu, whose country is widely believed to be the Middle East’s sole, if undeclared, nuclear power.

Jo Biddle and Gerard Aziakou/AFP/Expatica