Scrapped Iran nuclear deal 'would take decades to re-negotiate': John Kerry

Former Secretary of State John Kerry has warned if the United States walked away from the Iran nuclear deal, a new agreement would take decades to re-negotiate.

"If we pull back from what they have done, it will be 30 years before another president will ever sit down with Iranians to negotiate," Kerry said, speaking at the World Affairs Council at Villanova University in Philadelphia.

"Then we will be on track, if something goes wrong, of confrontation."

Kerry was heavily involved in, and often led, secret meetings that began negotiations with Iran to curb its nuclear programme.

Six world powers eventually agreed to lift sanctions and Iran agreed to open up its nuclear facilities to international monitors.

In January, US President Donald Trump said the nuclear deal must be "fixed" by May 12 or the United States will walk away.

Iran, which according to the UN atomic watchdog has been abiding by the deal since it came into force in January 2016, has repeatedly rejected plans to amend the agreement.

The European parties to the accord are desperate to save it and have been scrambling to find ways to persuade Trump not to rip it up.

Kerry has made few public comments since leaving office at the end of 2016. But he made some criticisms of Trump and his policies during his speech on Tuesday, as reported by Washington Post.

"Instead of responding to obvious needs, we see self, party and ideological interests trumping - no pun intended - the real interests of our nation," he said.

Kerry said previous generations of Americans had leaders "who actually stood up and led".

"Today we don't see that," he added. "We get early morning tweet storms. Diversions from reality, from the truth itself."