Donald Trump needs to rejoin the international nuclear deal he pulled out of earlier this year if he wants to hold talks with Iran’s leader, an adviser to President Hassan Rouhani has said.

The US president said on Monday that he would meet with Mr Rouhani without preconditions if the Iranian leader was willing.

Iranian leadership has previously ruled out one-on-one talks with Mr Trump after his decision to pull the United States out of the deal under which Iran was given relief from sanctions in return for curbs on its nuclear programme.

Donald Trump
Trump has recently met one-on-one with Kim Jong Un and Vladimir Putin (Evan Vucci/AP)

Iran’s semi-official ISNA news agency quoted political adviser Hamid Aboutalebi as saying that for talks to happen, the US needs to rejoin the deal.

Mr Aboutalebi said: “Those who believe in dialogue as a method of resolving disputes in civilised societies should be committed to the means.”

Speaking during a joint news conference with Italy’s premier Giuseppe Conte, Mr Trump said he would meet with the Iranians “anytime they want to”.

He said: “I’ll meet with anybody. There’s nothing wrong with meeting.”

The United States has also vowed to boost sanctions until Iran changes its regional policies, including its support for regional militant groups.

Rouhani recently warned the US that “war with Iran is the mother of all wars”, prompting an all-caps retort from Mr Trump.

He wrote on Twitter: “To Iranian President Rouhani. NEVER, EVER THREATEN THE UNITED STATES AGAIN OR YOU WILL SUFFER CONSEQUENCES THE LIKES OF WHICH FEW THROUGHOUT HISTORY HAVE EVER SUFFERED BEFORE. WE ARE NO LONGER A COUNTRY THAT WILL STAND FOR YOUR DEMENTED WORDS OF VIOLENCE & DEATH.”

He ended the message with a warning: “BE CAUTIOUS!”

Iranian foreign minister Mohammad Javad Zarif fired back with his own message that began, “COLOUR US UNIMPRESSED.”

Mr Trump tempered his threatening rhetoric two days later when he said his administration stands ready for Iran to come back to the negotiating table.

“We’re ready to make a real deal, not the deal that was done by the previous administration, which was a disaster,” he said.

Mr Trump paints himself as a master negotiator who is most effective when he meets with his counterparts face-to-face. He pointed to his recent one-on-ones with North Korea’s Kim Jong Un and Russia’s Vladimir Putin as examples of the benefits of such get-togethers.

“I believe in meeting,” he said, talking up the benefits of “speaking to other people, especially when you’re talking about potentials of war and death and famine and lots of other things.”

Asked whether he would set any preconditions for the meetings, Mr Trump was clear.

“No preconditions, no. If they want to meet, I’ll meet anytime they want, anytime they want,” he said. “Good for the country, good for them, good for us and good for the world. No preconditions. If they want to meet, I’ll meet.”

US secretary of state Mike Pompeo told reporters he was on board with the president’s invitation, saying Mr Trump “wants to meet with folks to solve problems”.

But he appeared to add several qualifications: “If the Iranians demonstrate a commitment to make fundamental changes in how they treat their own people, reduce their maligned behaviour, can agree that it’s worthwhile to enter in a nuclear agreement that actually prevents proliferation, then the president said he’s prepared to sit down and have a conversation with him.”