Iran has not diverted nuclear materials it declared to the International Atomic Energy Agency (IAEA) to make weapons, the UN watchdog has concluded.
Iran insists it has complied with all international inspection demands
But the IAEA said it could not rule out the existence of nuclear materials that had not been declared.
Iran has agreed to suspend its uranium
enrichment activities by 22 November, following talks with the European Union, officials in Tehran say.
Iran is facing a 25 November deadline to comply with an IAEA resolution.
In a confidential report, the UN nuclear watchdog said: "All the declared nuclear material in Iran has been
accounted for, and therefore such material is not diverted to prohibited activities."
A senior diplomat close to the IAEA said "prohibited activities" included possible work on weapons, Reuters news agency quoted him as saying.
But the report went on to say that doubt remained over Iran's nuclear programme.
"The Agency is, however, not in a position to conclude that there are no undeclared nuclear materials or activities in Iran," it added.
Iran agreed to suspend its uranium enrichment activities on Sunday, after talks with three European Union countries.
The EU offered Iran increased co-operation on trade and energy in exchange for the freeze.
Chief Iranian negotiator Hassan Rohani said Tehran would suspend "almost all" its enrichment activities until a long-term agreement on Iran's nuclear programme is reached.
Iran insists its nuclear activities are peaceful, but the US says they are part of a secret weapons programme.
Successful uranium enrichment could be seen as a key stage in the development of weapons-grade nuclear material.
The Vienna-based IAEA passed a resolution in September calling on Iran to stop enriching uranium.
The findings of the report are due to be reviewed by the IAEA's board of governors on 25 November - three days after the freeze is set to begin.
Correspondents say this new deal makes it unlikely that the US will refer Iran to the UN Security Council for possible sanctions.