The finding by the International Atomic Energy Agency Wednesday complicated diplomatic efforts to revive a landmark 2015 nuclear deal between Iran and major powers, including the United States.

Last month, all sides voiced hope a deal was within reach, but Iran is still insisting that the IAEA close the investigation into its past nuclear activities as part of any deal and diplomats have said they are now less confident of a renewed agreement.

"The recent report... is a rehash for political purposes of baseless issues from the past," Iran Atomic Energy Organisation spokesman Behrouz Kamalvandi said in a statement.

"Iran will present its well-founded legal responses" to the findings at the IAEA's next board of governors meeting in Vienna from September 12 to 16, he added.

In its report, the IAEA said it was "not in a position to provide assurance that Iran's nuclear programme is exclusively peaceful".

It said IAEA Director General Rafael Grossi was "increasingly concerned that Iran has not engaged with the agency on the outstanding safeguards issues during this reporting period and, therefore, that there has been no progress towards resolving them".

The IAEA has been pressing Iran for answers on the presence of nuclear material at three undeclared sites and the issue led to a resolution that criticised Iran being passed at the June meeting of the IAEA's board of governors.

Tehran, which maintains that its nuclear programme is exclusively peaceful, this week again insisted that the IAEA probe would have to be concluded in order to revive the 2015 deal on its nuclear programme with world powers.

- Deal hopes dwindling -

In another report also issued on Wednesday, the IAEA addressed Iran's decision in June to disconnect 27 cameras allowing the agency's inspectors to monitor its nuclear activities.

The removal of the cameras has had "detrimental implications for the agency's ability to provide assurance of the peaceful nature of Iran's nuclear programme," the report said.

Kamalvandi said the issue of the monitoring cameras would be addressed as part of a revived nuclear agreement.

But he stressed that the United States needed to meet its obligations too by lifting the economic sanctions imposed by then president Donald Trump after he unilaterally abandoned the deal in 2018.

"In order to restore the previous verification system, the parties to the agreement must abide by their commitments," Kamalvandi said.

The twin IAEA reports come as Tehran and Washington exchange responses to a "final" draft agreement drawn up by European Union mediators.

EU foreign policy chief Josep Borrell had expressed hope that with minor modifications the draft would prove acceptable to both sides, but on Monday hs said that recent exchanges had left him "less confident".

Washington said last week that Tehran's latest proposed changes to the text were "not constructive" and Borrell too voiced disappointment.

"The last answer I got, if the purpose is to close the deal quickly, it is not going to help it," he said.

A renewed deal would see more than one million barrels of Iranian oil back on international markets, bringing new relief to consumers hit by surging prices after Russia's invasion of Ukraine.