Brazil and Turkey have urged fellow members of the UN Security Council to heed a deal they struck with Iran over its nuclear programme.
Both were disappointed by proposals for new sanctions tabled a day after Tehran agreed to trade uranium for ready-enriched reactor fuel.
Iranian officials said major powers would be "discrediting" themselves if they ignored the hard-won deal.
The US-drafted text is backed by all five permanent (P5) council members.
They believe that Iran is trying to obtain a nuclear weapon, which Iran denies.
The new measures put before the UN foresee cargo ship inspections and new banking controls.
"Brazil and Turkey are convinced that it is time to give a chance for negotiations and to avoid measures that are detrimental to a peaceful solution of this matter," the foreign ministers of Brazil and Turkey said in the letter to the UN Security Council.
UN diplomats say that is an admonition to all sides, including Iran, not to over-react, and the P5 not to aggressively push for a vote on the sanctions resolution - so that there can be space and time for the Brazil-brokered deal to be implemented, says the BBC's UN Correspondent Barbara Plett.
On Monday, the three countries signed a deal in which Iran agreed to send low-enriched uranium to Turkey in return for enriched fuel for a research reactor.
Placing Iran's nuclear material in a third country was intended to act as a confidence-building measure by the major world powers to prevent Iran producing more highly-enriched, weapons-grade material.
A similar deal was suggested last year by the five permanent members of the Security Council - the US, France, UK, China and Russia - plus Germany, who have been negotiating with Iran over its nuclear programme.
But plans for a fourth set of UN sanctions against Iran over its nuclear programme were circulated among all 15 members of the Security Council on Tuesday.
US Secretary of State Hillary Clinton has dismissed Iran's deal as an attempt to deflect pressure. She said the five veto-wielding permanent members had agreed on a "strong" draft resolution.
A close adviser to Iranian President Mahmoud Ahmadinejad, Mojtaba Hashemi Samareh, has dismissed the new measures as illegitimate.
And the head of Iran's atomic energy organisation, Ali Akbar Salehi, has said newly-proposed sanctions on Iran will backfire.
"They won't prevail and by pursuing the passing of a new resolution they are discrediting themselves in public opinion," said Mr Salehi, who is also Iran's vice-president and the highest-ranking Iranian official to speak since the proposals were tabled.
"This [UN Security Council draft] resolution is the last effort by the West," he told Iran's semi-official news agency, Fars.
"They feel that for the first time in the world developing countries are able to defend their rights in the world arena without resorting to the major powers an that is very hard for them," he said.
Iran is also preparing a letter for the UN atomic watchdog, the International Atomic Energy Agency, officially notifying them of their deal with Turkey, Mr Salehi said.