Iranian, Brazilian and Turkish foreign ministers brokered the deal
Western states have given a cool response to Iran's announcement it will send uranium abroad for enrichment after talks with Turkey and Brazil.
The UN and Russia said the move was encouraging, but the US expressed concern at Iran's statement that it would continue to enrich uranium.
The US and the UK said work on a UN resolution imposing more sanctions on Tehran would continue.
The West suspects Iran's nuclear programme is aimed at making weapons.
Iran insists it is solely designed to meet its energy needs.
Tehran hopes the new agreement - in which it would ship 1,200kg (2,645lb) of low-enriched uranium to Turkey in return for higher-grade nuclear fuel for a research reactor - would avert new sanctions.
In a deal brokered by Turkey and Brazil, Iran said it was prepared to move uranium within a month of its approval by the so-called Vienna Group (US, Russia, France and the IAEA).
By Barbara Plett BBC UN correspondent
A key part of the Western strategy has been winning international consensus for a new round of sanctions.
Russia and particularly China have been reluctant to support such a move, they may now want to further delay the process until they see what the deal means in practice.
Here the UN's nuclear monitoring agency, the IAEA, will be crucial: a positive response would lend the agreement significant credibility.
Even if that doesn't happen, Turkey and Brazil have to be taken into account.
They are both current members of the Security Council, and while they couldn't block a new sanctions resolution, they could split the vote, which is what Iran wants.
In return, Iran says it expects to receive 120kg of more highly enriched uranium (20%) - a purity well below that used in the manufacture of nuclear weapons - within a year.
The deal does not address the central nuclear issues dealt with by successive UN Security Council resolutions - Iran's refusal to halt its enrichment programme.
The US reacted by saying it still had serious concerns over Iran's nuclear programme, although it did not reject the agreement.
The US is in the final stages of negotiating a fourth sanctions package with other UN Security Council members.
It said the Iranian government "must demonstrate through deeds - and not simply words - its willingness to live up to international obligations or face consequences, including sanctions".
"While it would be a positive step for Iran to transfer low-enriched uranium off of its soil as it agreed to do last October, Iran said today that it would continue its 20% enrichment, which is a direct violation of UN Security Council resolutions," said a White House statement.
Russia welcomed the deal, although President Dmitry Medvedev said further talks were needed on Iran's nuclear programme.
Meanwhile, French Foreign Minister Bernard Kouchner said there had been "some important progress" in talks at the Security Council on fresh sanctions against Tehran.
KEY POINTS OF THE DEAL
Iran will notify the IAEA of the details of the agreement within a week
If approved by the Vienna Group, Iran will ship 1,200kg of low-enriched uranium (LEU) to Turkey
The LEU will remain the property of Iran while in Turkey
Tehran and the IAEA may send observers to monitor its security
The Vienna group must then deliver 120kg of nuclear fuel to Iran within a year
Iran may request that Turkey return its LEU "swiftly and unconditionally to Iran
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