IAEA nations will discuss at the summit whether to vote on a resolution against Iran for its lack of cooperation.
The International Atomic Energy Agency (IAEA) has begun a three-day board meeting in Vienna to discuss Iran's nuclear programme.
The summit comes just days after Director-General Rafael Grossi held meetings in Tehran with the Iranian government in an attempt to improve cooperation.
A confidential report seen by The Associated Press showed that Iran defied international pressure to rein in its nuclear programme, and increased its stockpile of uranium enriched to levels needed to make a bomb.
Uranium, a naturally occurring radioactive element, has to be enriched "in order to produce fuel for certain types of nuclear reactors and nuclear weapons," the UN watchdog says. Under the IAEA's definition, one atomic weapon can be created when 42 kilograms of uranium enriched to 60% are further enriched to 90%.
IAEA nations will discuss at the summit whether to vote on a resolution against Iran. The move would be an embarrassment for Tehran's leaders, and a boost for supporters of taking a tough stance against Iran.
Several media outlets report that two confidential reports by the UN watchdog show that Iran offered not to expand its uranium which had been enriched to up to 60% purity, on the conditional offer that Western powers drop their push for the resolution against Iran.