Iranian President Hassan Rouhani said on Monday that America would pay a high price if U.S. President Donald Trump makes good on his threats to scrap the Iran nuclear deal.

Speaking in an exclusive interview with CNN’s Christiane Amanpour in New York, Rouhani said: “Exiting such an agreement would carry a high cost for the United States of America, and I do not believe Americans would be willing to pay such a high cost for something that will be useless for them.”

Rouhani said such an action by the Trump administration “will yield no results for the United States but at the same time it will generally decrease and cut away and chip away at international trust placed in the Unites States of America.”

The U.S. extended sanctions relief for Iran last week as part of the 2015 nuclear agreement, which Trump has described as “the worst deal ever,” but this is mainly procedural.

The real test comes in October when Trump will decide whether to certify that Iran is complying with the agreement. If he does not, Congress has 60 days to decide whether to reimpose sanctions waived under the deal.