"I don't think they want to take the consequences of not making a deal," Trump says.
Representatives of the two countries plan to hold a new round of talks in Geneva, Switzerland, on Tuesday, with Oman acting as mediator.
Donald Trump says he will be "indirectly involved" in this week's talks, and has previously threatened military action against Iran.
The United States and a number of European countries have expressed concern that Iran is developing nuclear weapons as part of its nuclear energy program, a claim Iran has dismissed.
