US President Donald Trump has threatened Iran with military action and economic sanctions if Tehran does not reach an agreement with Washington over its nuclear programme.

During a telephone interview with NBC, Trump also threatened “bombing” and “secondary tariffs” on Iran if the country did not make a deal with the US to ensure it did not develop a nuclear weapon.

“If they don’t make a deal, there will be bombing. It will be bombing the likes of which they have never seen before,” he noted US and Iranian officials are “talking.”

The comments came as Iranian President Masoud Pezeshkian revealed that Iran has rejected direct talks with the United States in its response to Trump's recent letter, though Tehran remains open to indirect negotiations through Oman and other intermediaries.

"While the response rules out the possibility of direct talks between the two sides, it states that indirect negotiations remain an option. It also emphasises that Iran has never shied away from engaging in dialogue," IRNA quoted Pezeshkian as saying during a cabinet meeting.

Iranian government spokeswoman Fatemeh Mohajerani confirmed that indirect negotiations with the US are now "on the agenda" as diplomatic tensions persist.

Her comments followed reports of an official Iranian jet flying to Oman with Tehran's response to Trump.

Foreign Minister Abbas Araghchi stated on March 27 that Tehran's official response had been sent.

"This official response fully outlines our views on the current situation and Mr. Trump's letter, which has been communicated to the other party," Araghchi told IRNA.

Trump's threats come amid reports of the US reinforcing military assets at its Diego Garcia base in the Indian Ocean, including B-52 bombers, raising concerns about potential military escalation.

Kamal Kharrazi, chairman of Iran's Strategic Council on Foreign Relations, dismissed Washington's latest diplomatic efforts as "psychological warfare."