The UN will make a key inspection of a plant near Qom on Sunday
US President Barack Obama has called the French and Russian leaders to consolidate their support ahead of a key UN nuclear inspection in Iran.
The White House said Nicolas Sarkozy and Dmitry Medvedev fully backed a new UN plan on Iran's nuclear programme.
The plan would see international powers refine Iran's uranium in return for affirmation that Tehran will not produce nuclear weapons.
The UN will inspect a recently revealed nuclear plant near Qom on Sunday.
It will be the first time monitors from the UN's nuclear watchdog, the International Atomic Energy Agency (IAEA), have been allowed access to the plant.
The White House said Mr Obama had telephoned Mr Sarkozy and Mr Medvedev to thank them for their countries' roles in developing the IAEA plan on Iran's enriched uranium.
NUCLEAR FUEL CYCLE
Mined uranium ore is purified and reconstituted into solid form known as yellowcake
Yellowcake is converted into a gas by heating it to about 64C (147F)
Gas is fed through centrifuges, where its isotopes separate and process is repeated until uranium is enriched
Low-level enriched uranium is used for nuclear fuel
Highly enriched uranium can be used in nuclear weapons
Mr Obama thanked Mr Sarkozy for France's close cooperation and Mr Medvedev for Russia's leadership on the issue.
Under the deal most of Iran's uranium would be exported to the IAEA and sent to Russia for enrichment and on to France for further refinement.
Iran would get the fuel it needs for its research reactor in Tehran, but this would not be sufficiently enriched to make a bomb.
Iran has said it will respond to the offer by the middle of next week.
The White House said the US, French and Russian leaders had all "affirmed their full support" for the deal.
Iran says its nuclear programme is for purely peaceful purposes but the revelation of the existence of the new plant near Qom had increased fears in the West about Tehran's intentions.
BBC Tehran correspondent Jon Leyne says Iran announced the existence of the new plant last month apparently because Western intelligence had already discovered it.
Our correspondent says that Iran would have had plenty of time to remove anything that might be incriminating.
He adds that there has also been a setback in Iran to the IAEA deal. The speaker of parliament and two other senior parliamentarians have expressed opposition to Iran allowing its enriched uranium to leave the country.
However, the head of the IAEA, Mohammed ElBaradei, has said he hopes there will be a positive answer from Iran.
"Approval of this agreement will signal a new era of co-operation," he said on Friday.