Former Secretary of State John Kerry on Monday warned the US Congress that it would be "extraordinarily dangerous" for it to reject the Iran nuclear deal that he helped broker.

President Donald Trump last month decertified Iran's compliance with the 2015 agreement, but stopped short of scrapping the deal outright, instead handing the issue over to Congress.

Kerry told the Chatham House international affairs think tank in London that the decision "was clearly made without relevance to any fact whatsoever" and criticised the involvement of Congress.

"It's been flipped over to the Congress with instructions, you guys fix it.

"How the US Congress, which wasn't part of the negotiations, which isn't certified to be part of the negotiations, fixes an agreement which is working is beyond me," he added.

"What President Trump regrettably has done by his invective against the deal, he's polluted the pool in a way that whatever Congress does is going to be interpreted as their effort to kill the deal through the back door."

Congress was given 60 days to decide whether to reimpose sanctions that were lifted in return for Tehran abandoning its nuclear ambitions.

Kerry said there was a "great danger" that Congress could act unilaterally to alter the deal, narrowing Iran's room for manoeuvre and "creating a downward spiral that becomes extraordinarily dangerous."

"It would be a gigantic, historic mistake when dealing with nuclear weapons to allow anyone's politics to get in the way and break apart an agreement that is preventing a country from pursuing a nuclear weapon," he added.

Opponents of the deal claim that it does not go far enough to prevent Tehran from getting a nuclear weapon, and point to Iran's recent missile launches.

Source: AFP