US President Donald Trump denounced the Iran nuclear deal as an "embarrassment" on Tuesday, in the latest sign that he plans to tear up or renegotiate the landmark accord.

"Frankly, that deal is an embarrassment to the United States, and I don't think you've heard the last of it," Trump told the UN General Assembly.

"Believe me. It is time for the entire world to join us in demanding that Iran's government end its pursuit of death and destruction."