Mr Amano is taking a tougher line than his predecessor, Mohamed ElBaradei
Iran is not co-operating with the UN nuclear watchdog's investigation into the country's nuclear programme, the new head of the agency has said.
Iran's insistence its nuclear programme was peaceful could not be confirmed, Yukiya Amano told the International Atomic Energy Agency (IAEA) in Vienna.
Mr Amano is taking a more critical line than his predecessor, analysts say.
The news is likely to strengthen calls for sanctions on Iran. Iran's foreign minister has rejected Mr Amano's claim.
"The agency continues to verify the non-diversion of declared nuclear material in Iran, but we cannot confirm that all nuclear material in Iran is in peaceful activities because Iran has not provided the agency with the necessary co-operation," Mr Amano said.
He was speaking at a 35-nation board meeting of the IAEA in Vienna, the first since he took over as the head of the organisation in December.
Iranian Foreign Minister Manouchehr Mottaki rejected Mr Amano's statement.
"We have fully co-operated with the agency. This co-operation will continue," he told journalists.
The BBC's Bethany Bell in Vienna says Mr Amano's address, and a report leaked earlier this month, are much more critical of Iran than the IAEA had been under its former head, Mohamed ElBaradei.
US ambassador Glyn Davies: 'We've worked very hard to reach out'
This could strengthen calls for tough sanctions on Iran, which have so far been resisted by UN Security Council members Russia and China, our correspondent says.
Meanwhile, Glyn Davies, US ambassador to the IAEA, told the BBC that the existing sanctions on Iran had "an effect in slowing Iranian nuclear programme".
He said it was important that in addition "to continuing to try to find ways to reach out to Iran" to at the same time "put pressure on them".
Iran insists its nuclear enrichment programme is for peaceful civilian use. It says it wants to increase the enrichment of uranium it has for power generation and for medical use.
It accuses the IAEA of being influenced by the US.
But critics say that Iran's attempts to enrich uranium to 20% are the first step to creating weapons-grade nuclear material.
Last year, Iran revealed a previously unknown nuclear facility in the mountains near the city of Qom.
Tehran has said it is planning 10 further sites to enrich uranium.
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