Iran's President Ebrahim Raisi said Wednesday that his country was "transparent" about its nuclear activities, the day after the UN atomic watchdog criticised it for lack of cooperation.

"The Islamic Republic of Iran's serious cooperation with the International Atomic Energy Agency is a clear example of Iran's will to be transparent about its nuclear activities," Raisi told European Council chief Charles Michel by phone, according to an Iranian presidency statement.

"Of course, if the IAEA has a non-constructive approach, it's unreasonable to expect a constructive response from Iran," Raisi added.

"What's more, non-constructive actions of course upset the negotiation process."

On Tuesday the IAEA said its monitoring at Iranian nuclear sites had been "seriously undermined" by Tehran's suspension of some inspections since February.

The exchange of words comes as talks remain locked in Vienna on saving the 2015 deal with world powers that gave Iran relief from international sanctions in return for curbs on its nuclear programme.

The deal formally known as the Joint Comprehensive Plan of Action was torpedoed by former US president Donald Trump's unilateral decision to withdraw the United States from it in 2018 and impose sanctions.