Washington has said it wants to pressure Iran to change its behaviour by taking away all revenue Tehran generates from crude sales, part of the confrontational approach adopted by President Donald Trump, who pulled out of the historic nuclear pact in May.

"These are exaggerated statements that can never be implemented," Rouhani told reporters in Bern, after holding talks with Swiss authorities on a range of issues, including the nuclear deal.

"Such a scenario would mean the US was imposing its imperialist policy in flagrant violation of international law," he said.

"This is really a baseless fantasy," he added, condemning an "unjust" scenario in which all oil producers are allowed to export crude except Iran.

Washington insists the world has enough spare oil capacity to replace Iranian crude, and Trump has said that he has persuaded Saudi Arabia to balance the market by boosting its own production.

- 'Unparallelled success' -

The international community still overwhelmingly backs the nuclear deal, which opened new opportunities to deepen economic relations with Iran.

But many believe nations will have to sever ties once Washington reimposes sanctions -- to avoid losing access to US markets and financing.

Swiss President Alain Berset, speaking next to Rouhani, called the nuclear deal "an unparallelled success" that needed to be preserved.

Switzerland -- where significant parts of the pact known as the Joint Comprehensive Plan of Action were negotiated -- will work to ensure that future US sanctions do not target any humanitarian goods, Bern said in a statement.

Rouhani said the "indiscriminate sanctions imposed against a great nation was the greatest violation of human rights imaginable."

The nuclear deal was signed in Vienna, where Rouhani will hold further talks on Wednesday.

Then on Friday in the Austrian capital, Iran's foreign minister will meet the top envoys from the five powers still party to the JCPOA -- Britain, China, France, Germany and Russia -- according to Iranian state media.

The Iranian president reiterated Tehran's position that it would remain committed to the JCPOA so long as the country can enjoy its "benefits".

"The nuclear agreement was truly an important achievement and it is in the interest of the world that this agreement be preserved for international peace," Rouhani said.

The least cordial moment during the public appearance by the two leaders concerned Israel.

Berset noted that in bilateral talks he had underscored "the need to recognise the state of Israel," prompting a reply from Rouhani that Tehran viewed "the Zionist regime as an illegitimate regime," responsible for fostering conflict in the region.

Separately, the two nations inked deals on future cooperation in the health and science sectors.