US President Donald Trump has threatened Iran with bombings and secondary tariffs if Tehran does not come to an agreement with Washington over its nuclear program.

In a telephone interview with NBC News, Trump said US and Iranian officials are talking but did not elaborate.

In his first 2017-21 term, Trump withdrew the US from a 2015 deal between Iran and world powers that placed strict limits on Tehran’s disputed nuclear activities in exchange for sanctions relief. Trump also reimposed sweeping US sanctions.

Since then Iran has far surpassed the agreed limits in its escalating program of uranium enrichment. Tehran has so far rebuffed Trump’s warning to make a deal or face military consequences.

Iran sent a response through Oman to Trump’s letter in which he urged Tehran to reach a new nuclear deal.

Western powers accuse Iran of having an clandestine agenda to develop nuclear weapons capability by enriching uranium to a high level of fissile purity, above what they say is justifiable for a civilian atomic energy program. Tehran says its nuclear program is wholly for civilian energy purposes.