The crux of the July 2015 pact between Iran and six major powers - Britain, China, France, Germany, Russia and the United States - was that Iran would restrict its nuclear program in return for relief from sanctions that have crippled its economy.
But by picking CIA Director Mike Pompeo, an avowed Iran hawk, to succeed Tillerson as secretary of state, Trump sent a clear message that Washington was hardening its stance as a May 12 deadline approaches for the possible reimposition of USA sanctions.
Many of Trump's top national security aides, like Tillerson, have argued that the United States is better off with the Iran nuclear deal than without it.
"I think it's awful, I guess he thinks it was OK", Trump said. I guess he thought it was okay.... "It's Trump's line", said another European diplomat.
In a statement on January 12, U.S. President Donald Trump gave Europeans only 120 days to agree to an overhaul of the nuclear agreement and said if the text of the deal is not revised he would unilaterally withdraw the U.S. from it.
Trump administration officials say the talks are at an "advanced" stage entering their latest round of meetings in Berlin.
According to Axios, senior Israeli officials claim the president will not work with Germany, France, and the United Kingdom on the Iran deal unless harder measures are taken to ensure the Middle Eastern country does not obtain nuclear weapons by his May 12th deadline to change the agreement. Hook was an influential figure on Tillerson's staff and it's unlikely he will stay on under Pompeo.
The US president added that for those reasons, he has "determined it is necessary to continue the national emergency declared with respect to Iran and to maintain in force comprehensive sanctions against Iran to respond to this threat".More news: School violence remembered as thousands of shoes placed before US Congress
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"The officials say Trump told Netanyahu that until now the three European powers only proposed "cosmetic changes" that he doesn't find satisfactory".
The Iran nuclear deal was agreed to during the Obama administration.
Critics of the nuclear agreement welcomed Tillerson's departure. It lifts sanctions placed on Iran in exchange for Iran abandoning its nuclear weapon ambitions.
It is unclear how Mike Pompeo becoming US secretary of state may affect the Iran nuclear deal. "However, my understanding is he doesn't want the deal to disappear", said a former senior US official. A US withdrawal could wreck the agreement, scaring off European investment that Iran saw as a key reward for agreeing to limit its uranium enrichment and other nuclear work.
The move is the latest in a series of measures by Washington aimed at dealing with one of the greatest diplomatic hurdles before Donald Trump's administration, to contain the regime in Iran while keeping up to America's global commitments within the JCPOA.
"The North Koreans will wonder about whether one can have credible negotiations with the United States", said a former senior US official.
If the deal unravels and Iran concludes it has no economic incentive to hold back on its nuclear work, then Tehran could expel United Nations inspectors and head down a fast track to building nuclear weapons - possibly in a matter of months.