Tehran: Iran's envoy to the International Atomic Energy Agency has urged the UN watchdog to "avoid perturbing the climate of cooperation," saying talks over Tehran's controversial nuclear programme would continue.

Ali Asghar Soltanieh was speaking after two days of fruitless visit to Iran by IAEA inspectors raised tensions, with Russia warning of "catastrophic" consequences if it leads to a military attack on the country.

"During the past two days, we raised technical and legal matters. Technical answers were provided to the agency's questions," Soltanieh said on Wednesday.

"This posture of cooperation and dialogue will continue, and we advise (the IAEA) to avoid perturbing the climate of cooperation."

"Proposals were made" to advance cooperation between Iran and the IAEA, "but to reach a final accord, we need more time. And we have agreed to continue discussions."

The IAEA said it had gone into the two-day visit to Tehran, and another inconclusive one last month, in a "constructive spirit," but that no agreement had been reached on efforts to elucidate Iran's nuclear activities.

The UN watchdog said there was no agreement with Iran "at this point in time" on holding further talks.

Despite requests, "we could not get access" to a military site in Parchin where suspected nuclear warhead design experiments were conducted, team leader and chief inspector Herman Nackaerts said on returning to Vienna.

Referring to Parchin, Soltanieh said: "For every visit, it is necessary to fix a framework and rules taking into consideration both parties."

Talk of possible military action against Iran by Israel, with or without US help, had lent urgency to diplomatic efforts to lower tensions.

The United States and Europe have been ramping up economic sanctions on Iran since November, when the IAEA published a report crystallising -- though not entirely validating Western suspicions it was pursuing nuclear weapons research in Parchin and elsewhere.

Iran has repeatedly said the sanctions will not deter it from its nuclear ambitions, and it has threatened to strike back at any military action, possibly by closing the strategic Strait of Hormuz.