UNITED NATIONS - The U.N. Security Council, at a summit chaired by U.S. President Barack Obama, unanimously approved a resolution on Thursday that envisaged a world without nuclear weapons.

The resolution also called for an end to the proliferation of atomic weapons but did not name either Iran or North Korea, which western countries regards as the top atomic threats.

However British Prime Minister Gordon Brown and French President Nicolas Sarkozy specifically called for tougher sanctions against Iran for defying U.N. demands to halt sensitive nuclear work.

Obama presided over the two-hour meeting at U.N. headquarters in Manhattan, the fifth time the council met at the head-of-state level and the first time it was chaired by a U.S. president since the panel was formed in 1946.

I called for this (summit) so that we may address at the highest level a fundamental threat to the security of all peoples and all nations -- the spread and use of nuclear weapons, Obama said.

Obama said the next year would be absolutely critical in determining whether efforts to stop the spread and use of nuclear weapons were successful.

The U.S.-drafted resolution called for further efforts in the sphere of nuclear disarmament to achieve a world without nuclear weapons and urged all countries that have not signed the 1970 nuclear Non-Proliferation Treaty (NPT) to do so.

Critics of the resolution said it failed to include mandatory provisions that would have required nuclear weapons states to take concrete disarmament steps.

Chinese President Hu Jintao made clear that Beijing had no plans to scrap its nuclear arsenal.

We will continue to keep our nuclear capabilities at the minimum level required for national security, and make efforts to advance the international disarmament process, Hu said.

Some U.N. diplomats said the nuclear powers were more interested in non-proliferation than disarming.

'MORAL AUTHORITY'

But Mohamed ElBaradei, the Nobel Peace Prize laureate head of the U.N. International Atomic Energy Agency, said non-proliferation and disarmament were inextricably linked.

By demonstrating their irreversible commitment to achieving a world free from nuclear weapons the weapons states ... gain the moral authority to call on the rest of the world to curb the proliferation of these inhumane weapons, he said.

All five permanent Security Council members -- the United States, Russia, China, Britain and France -- have atom bombs.

Signatories to the NPT without nuclear arsenals have complained for decades that the world's official nuclear powers have failed to live up to their commitments while seeking to prevent other countries from joining the nuclear club.

The United States refrained from naming countries in the resolution to avoid disagreements with Russia and China, U.N. diplomats said. But Brown and Sarkozy had no such qualms in their speeches to the council.

As evidence of its breach of international agreements grows, we must now consider far tougher sanctions together, Brown said.

The United States and Germany are among Western powers that have called for targeting Iran's energy sector.

If we have the courage to affirm and impose sanctions together against those who violate resolutions of the Security Council, we will be lending credibility to our commitment toward a world with fewer nuclear weapons, Sarkozy said.

Iran says its nuclear program is peaceful and rejects U.N. demands to halt it. In a statement responding to the council debate, Iran said it was open to talks but warned that they would fail unless the West dropped illegal demands.

Diplomats and analysts said the U.S. decision to organize the summit highlighted a sharp shift on disarmament policy taken by the Obama administration. Obama's predecessor, George W. Bush, angered many NPT members by ignoring disarmament commitments undertaken by previous U.S. governments.

The resolution also urged other states outside the NPT to join disarmament efforts to help rid the world of atom bombs.

These states, not named in the resolution, are Pakistan and India, which have not signed the NPT but are known to have atomic weapons, and Israel, which neither confirms nor denies having nuclear arms but is believed to have a sizable arsenal.

North Korea withdrew from the NPT in 2003 and tested its first nuclear device in 2006 and another earlier this year.

The resolution also called on U.N. member states to ratify a treaty banning nuclear tests and supported negotiations on a pact banning the production of fissile material for warheads.

(Editing by Alan Elsner)

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