Mr Elbaradei said no progress had been made in talks with Iran
Investigations into Iran's nuclear programme will reach a "dead end" unless Tehran starts to co-operate, the UN nuclear chief has warned.
Mohamed El Baradei told governors of the International Atomic Energy Agency (IAEA) that there had been no movement on issues that needed to be clarified.
He said he was "disappointed" with Iran's rejection of a deal that would see its uranium processed overseas.
He spoke ahead of an IAEA vote on a resolution critical of Iran.
In September Iran was revealed to have a second uranium enrichment facility, deepening Western fears about the nature of its nuclear ambitions.
Iran says its nuclear programme is for peaceful energy purposes, but the US and other nations say its is seeking nuclear weapons.
Addressing IAEA governors in Vienna, Mr El Baradei said his inspectors had made no progress on areas which needed to be clarified in order to verify the peaceful nature of Iran's nuclear programme.
"It is now well over a year since the agency was last able to engage Iran in discussions about these outstanding issues," he said.
"We have effectively reached a dead end, unless Iran engages fully with us."
Tehran's late declaration of a second nuclear fuel enrichment facility had, he said, reduced "confidence in the absence of other nuclear facilities under construction in Iran which have not been declared".
And he called Iran's failure to agree to a US-backed plan under which its low-enriched uranium would be shipped overseas for processing into fuel disappointing.
The plan is seen as a way for Iran to get the fuel it needs, while giving guarantees to the West that it will not be used for nuclear weapons.
The BBC's John Leyne says that after years of taking a conciliatory tone, Mr El Baradei appears to have lost patience with the Iranians.
The IAEA chief, who steps down next month, spoke ahead of the vote on a resolution calling on Iran to halt construction of the recently-declared enrichment plant.
According to Reuters news agency, it also calls on Iran to comply with Security Council resolutions demanding a halt to uranium enrichment activity and allow IAEA inspectors access to its facilities.
If approved, it would be the first IAEA action against Iran in almost four years. The vote is expected either later in the day or on Friday.