The UN's atomic watchdog has adopted a resolution calling on Iran to halt nuclear fuel development, which it resumed this week.
Iran says its nuclear programme is for purely peaceful purposes
The statement leaves the door open for further talks if Iran complies. It does not call for action by the UN Security Council, according to reports.
Iran denounced the resolution as a tool to put it under pressure and vowed it would not bend.
Iran denies claims it is secretly trying to develop nuclear arms.
The resolution expresses "serious concern" over Iran's resumption of work at its uranium conversion plant at Isfahan on Monday, the Associated Press news agency reports.
The statement said "outstanding issues relating to Iran's nuclear program have yet to be resolved, and that the [International Atomic Energy] agency [IAEA] is not yet in a position to conclude that there are no undeclared nuclear materials or activities in Iran", AP said.
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
The IAEA asked its chief, Mohamed ElBaradei, to report on Iran's compliance by 3 September.
The resolution did not call for the case to be referred to the Security Council, which has the power to impose sanctions on Iran.
The IAEA's 35-member governing body met in emergency session for the past three days after Iran ended a nine-month suspension of work at Isfahan.
Iran insists it needs nuclear power as an alternative energy source, but Western nations fear it has plans to produce nuclear weapons.
The BBC's Emma Jane Kirby in Vienna, home to the IAEA's headquarters, says the US and Britain are calling for tough action against Iran.
Washington is calling for the UN to impose economic sanctions on Iran, on the grounds that Iran hid its uranium enrichment programme for 18 years.
But some countries fear a too heavy-handed approach could isolate it, as was the case with North Korea, and are finding it hard to agree, our correspondent says.
Cyrus Nasseri, Iran's chief negotiator at the IAEA talks, angrily criticised the resolution.
"It is evident that the motive is to apply pressure.
"Fortunately, Iran will not bend. Iran will be a nuclear fuel producer and supplier within a decade," AP quoted him as saying.
He has also warned the US and EU against referring Tehran to the UN Security Council.
"I think that would be a grave miscalculation by the US and particularly by Europe to move towards the path of confrontation," he said.
"There is no legal base whatsoever to go to the Security Council. If it is, it is by political choosing and it will be [a] big, big mistake."