U.S. President Donald Trump warned that Iran would face a “very bad day” if it fails to reach an agreement with the United States over its nuclear programme.

In a post on social media, Trump said he preferred to reach a deal but added that if no agreement was achieved, “it will be a very tough day for that country, and unfortunately for its people.”

Trump denied any disagreement with U.S. Chairman of the Joint Chiefs of Staff General Daniel Cain over how to handle Iran, calling reports of military opposition to a confrontation “fake news.”

He said Cain, like other military leaders, does not want war but “knows how to win if asked to do so,” praising his expertise and knowledge of the Iran file.

Trump stressed that he has the final say on any potential military action, saying he prefers a diplomatic solution, “but if a deal is not reached, the response will be harsh.”

There was no immediate comment from Iran.