Donald Trump has confirmed he's not going to certify a deal with Iran, which he's previously described as the worst deal ever.

Iran has been able to carry on nuclear research saying it wants the technology for peaceful purposes.

But the US President rejects that.

And he's calling Iran the world's biggest sponsor of terrorism.

"Our participation can be cancelled by me as president at any time. As we have seen in North Korea the longer we ignore a threat, the worse that threat becomes."

His decision puts the US at odds with the other countries which have signed up to the agreement.

The Iranians have stated that they are following the rules which has been agreed with by Russia, the European signatories and also the International Atomic Energy Agency.

But it doesn't mean the agreement is dead in the water as Trump can choose not to certify it at this time and leave the longer term decision to congress.