The UN nuclear chief has made a plea for Iran and the European Union to keep their nuclear talks alive.
Mohamed ElBaradei made the comments as a non-proliferation conference opened at the United Nations on Monday.
He also urged Iran to refrain from uranium enrichment activities.
The Iranian crisis has developed into a serious threat to the nuclear Non-Proliferation Treaty (NPT), which, since 1970, has mandated the world to fight against the spread of nuclear weapons.
Both ElBaradei and UN Secretary-General Kofi Annan warned in speeches opening the conference that the treaty is out of date in the face of new threats and technologies and needs to be fixed.
In comments about the EU's efforts to win guarantees that the Islamic republic will not make nuclear weapons, ElBaradei told reporters: "I hope that both parties will continue to talk."
"I would hope that the Iranians will not take any unilateral decisions to initiate any activities that now are currently suspended. I think that any future move has to be agreed between both parties."
German Foreign Minister Joschka Fischer said on Monday that any resumption of enrichment activities would lead to an end of Iran's nuclear talks with EU negotiators Britain, France and Germany.
In response to Fischer's comments, a senior Iranian nuclear official said Iran had no plans for the time being to resume uranium enrichment.
Isfahan, south of Tehran, hosts
a nuclear enrichment plant
"As the secretary of the supreme council for national security [Hassan Rowhani] has said previously, our decision does not concern any resumption of enrichment, our discussions concern the uranium conversion facilities in Isfahan," said council spokesman Ali Agha Muhammadi.
"No decision has been taken for the time being."
He added: "I hope the patience and seriousness of the Islamic republic will enable the cleansing of the poisoned atmosphere created by the United States, so that we can continue our talks with the European Union."
Uranium conversion involves turning uranium ore into UF6 gas. That gas can be fed into cascade sequences of centrifuges that refine out enriched uranium to be used as fuel for atomic power reactors or what can be the explosive core of a nuclear weapon.
Conversion is covered by a freeze Iran agreed to in November 2004 to kick-start negotiations with the European trio aimed at easing international fears that Tehran is seeking the bomb.
ElBaradei said the EU-Iran talks were in a "delicate phase - no question about it", adding that he had been talking with both sides.
Nuclear crises in Iran and North Korea, the discovery of an international smuggling ring supplying their programmes, and the threat of atomic terrorism are among recent developments leading to doubts about whether the NPT is working.
IAEA's ElBaradei said EU-Iran
talks were at a critical stage
"The plain fact is that the [non-proliferation] regime has not kept pace with the march of technology and globalisation, and developments of many kinds in recent years have placed it under great stress," Annan said.
The UN chief said the international community had to act to strengthen the NPT before "the gap between promise and performance becomes unbridgeable".
North Korea kicked out inspectors from ElBaradei's International Atomic Energy Agency (IAEA) in December 2002, withdrew from the NPT the following month, and now claims to have made atom bombs.
Annan said the Vienna-based IAEA should be given more authority to inspect the nuclear programmes of states that were party to the NPT by making an additional protocol so that wider inspections applied to all.
He also referred indirectly to Iran, saying the non-proliferation regime "will not be sustainable if scores more states develop the most sensitive phases of the fuel cycle and are equipped with the technology to produce nuclear weapons on short notice".
He added: "An important step would be for former Cold War rivals to commit themselves, irreversibly, to further cuts in their arsenals, so that warheads number in the hundreds and not the thousands."