Iran's President Hassan Rouhani said Wednesday the leak of an audio recording of his foreign minister sought to sow domestic "discord" during talks aimed at reviving a nuclear deal.

The controversial comments by top diplomat Mohammad Javad Zarif, in which he said the military was too influential in diplomacy, were leaked as Iran and world powers are engaged in talks on reviving a 2015 nuclear accord.

The talks, in Vienna, seek to return the United States to the agreement -- which Washington abandoned under former president Donald Trump -- and persuade Tehran to comply with nuclear obligations it retreated from in retaliation.

"Stealing a document, a tape, it is something that has to be investigated," President Rouhani told a cabinet meeting in televised remarks.

"Why (was it leaked) at this time? In my opinion, this tape ... could have been published a week ago as well." 

But "it was published right when the Vienna (talks) were at the height of their success, so that it creates discord inside" Iran, he emphasised.

"We can only lift sanctions through unity".

Not government views

The 2015 accord was hammered out during Rouhani's first term following lengthy negotiations led by Zarif.

The agreement promised Iran sanctions relief in exchange for limits on its nuclear programme.

But the deal started to unravel in 2018 when Trump pulled out of it and re-imposed sanctions, followed by Iran beginning to ramp up nuclear activities in response a year later.

Zarif has been under fire from conservatives since the three-hour audio tape was published on Sunday.

Comments he made about Qasem Soleimani, the commander of the Revolutionary Guards' foreign operations arm who was killed in a US air strike last year, hit a particular nerve.

"In the Islamic republic the military field rules," Zarif said in the audiotape, quoted by the New York Times. "I have sacrificed diplomacy for the military field rather than the field servicing diplomacy."

Rouhani praised Zarif for his track record and achievements, but also set out his own position on the relationship between Iran's military and diplomacy.

"The (military) field and diplomacy are not two fields against each other," Rouhani said.

Some of the views in the recording "are not the views of the government or the president. Any minister or official might have some views" of their own, the president said.

"If someone thinks that it is (a choice between) the (military) field or diplomacy, foreign policy or defensive policy, or that the (military) field must succeed or the negotiations -- this is not an accurate thing to say," the president said. 

"Two hands ultimately come together and do one thing," he said, emphasising that there is a "system and a framework" of discussing issues in both fields in Iran's Supreme National Security Council.

"In a free country like Iran we freely express our opinions in our meetings," Rouhani said.