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 where all oil producers are allowed to export crude except Iran.

Washington has said it is confident 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.

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.

Rouhani and Swiss President Alain Berset both underscored the importance of the nuclear deal, known as the Joint Comprehensive Plan of Action, substantial parts of which were negotiated in Switzerland.

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