Former Secretary of State John Kerry has reportedly engaged in clandestine diplomacy with a top Iranian official in an attempt to salvage the nuclear deal framework.

Kerry, who brokered the Iran deal for the Obama administration, met with Foreign Minister Javad Zarif about two weeks ago at the United Nations in Manhattan, a person briefed on the meetings told the Boston Globe.

The meeting was their second in two weeks, and came amid a whirlwind of meetings between Kerry and German President Frank-Walter Steinmeier, European Union official Federica Mogherini, and French President Emmanuel Macron.

President Donald Trump has threatened to reimpose sanctions on Iran at the next deadline for certifying Iran's compliance with the deal, which comes on May 12.

Then-Secretary of State John Kerry (left) is seen with Iranian Foreign Minister Mohammad Javad Zarif in 2015. Kerry met with Zarif about two weeks ago for secret talks in New York

Kerry has also been meeting with German President Frank-Walter Steinmeier (left) and French President Emmanuel Macron (right) in attempts to salvage the Iran deal

Kerry's flurry of clandestine diplomacy highlights his desperation to save the Iran nuclear deal, which he sees as a signature achievement.

The deal, between Iran and the five permanent members of the US security council, plus Germany and the EU, saw Iran agree to halt its nuclear weapons program for a decade in exchange for the lifting of economic sanctions.

Kerry's involvement in trying to preserve the deal after leaving office came as a surprise to foreign policy experts.

'It is unusual for a former secretary of state to engage in foreign policy like this, as an actual diplomat and quasi-negotiator,' Michael O'Hanlon, a foreign policy expert at the Brookings Institution, told the Globe.

'Of course, former secretaries of state often remain quite engaged with foreign leaders, as they should, but it's rarely so issue-specific, especially when they have just left office.'

Kerry and Zarif are seen together in 2016. Kerry brokered the Iran nuclear deal for the Obama administration and is desperate to see it salvaged in spite of Trump's threats

The shadowy diplomacy will raise questions of a violation of the Logan Act, which prohibits private citizens acting on behalf of the United States during a dispute with foreign governments.

But the obscure 18th century law has never been used to prosecute anyone - although it was raised to criticize Mike Flynn for his discussions with the Russian ambassador after the 2016 election.

Macron, whom Kerry met with in New York and Paris, in meetings conducted in both English and French, has been actively lobbying Trump to remain in the Iran deal.

The French president said this week that that leaving the deal could mean war.

Meanwhile, Israeli President Benjamin Netanyahu has been pushing Trump to take a more aggressive posture toward Iran, Israel's archenemy.

This week Netanyahu gave a presentation claiming he had proof that Iran 'lied' about its past nuclear weapons program.

On Thursday, Zarif threated to withdraw from the nuclear deal, saying Iran will not 'renegotiate or add onto' the deal.

The five-minute video shows Zarif behind his desk, delivering his message on the deal. He offers background first about the deal before laying into Trump and criticizing Europe for offering 'the United States more concessions from our pocket.'

'On 11 occasions since, the U.N. nuclear watchdog has confirmed that Iran has implemented all of its obligations,' Zarif, who studied in the U.S., says in American-accented English. 'In contrast, the U.S. has consistently violated the agreement, especially by bullying others from doing business with Iran.'