US President Donald Trump has warned Tehran again that it could face “very serious consequences” if it fails to reach a deal on its nuclear program.

US President Donald Trump said the United States and Iran must reach a deal, saying it could happen next month.

He added that if a deal is not reached, he will move to a second round of action, which would be “very, very tough” for Iran.

Speaking to the media, Trump stressed the importance of reaching a deal.

"It is important to reach an agreement with Iran; otherwise, the situation will be very, very difficult. If no agreement is reached, the situation in Iran will be very, very difficult," he said.

"We must reach an agreement; otherwise, the situation will become even more complicated and difficult," he told reporters.

Asked if the Israeli prime minister had asked him to end the talks, he said, “We haven’t talked about that. But I will talk to them if I want to.”

The president said the Iranians “should have agreed in the first place, so we went into Operation Midnight Hammer because they couldn’t do that. If they don’t reach an agreement now, it will be very difficult for Iran.”

Iran and the United States resumed talks last week in the Omani capital of Muscat.