It also would indicate that the United States would be willing to renegotiate agreements with every new administration, giving other countries reason to hesitate on negotiations if they felt future leadership would give them a better deal, Mogherini added.
Senior U.S. officials, European allies and prominent U.S. lawmakers have told Trump that refusing to certify the deal would leave the U.S. isolated, concede the diplomatic high ground to Tehran, and ultimately risk the unraveling of the agreement. Iran has always insisted that its nuclear program is for peaceful purposes and denies it has aimed to build an atomic bomb. North Korea's leaders, meanwhile, would have little incentive to negotiate a nuclear disarmament if they see the Iran deal collapse, he said. Tillerson is expected to reach out to other members of Congress in coming days to brief them on the administration's intentions on the nuclear deal.
She noted that the worldwide community, including the European Union and other USA allies, will continue to abide by the deal even if Trump chooses not to certify Iran's compliance, something which has been confirmed eight times by the global Atomic Energy Agency (IAEA). In effect, it would be walking away unilaterally.
"Tomorrow, the president will deliver remarks announcing the (Iran) strategy to the country, ?"
The Foreign Office said Johnson also spoke to Zarif and will meet Ali Akhbar Salehi, Iran's vice president and head of its nuclear agency, in London on Wednesday.
Mr. Trump has until Sunday to decide whether to recertify that Iran is in compliance with the Obama-era nuclear agreement, which limits Iran's nuclear program.
"The perception is that, look, Gaddafi gave his up and he's dead, and Iran gave theirs up and the United States didn't comply with the agreement".
"The decertification is an essential first step to persuading the Europeans that the alternatives to fixing the deal could be President Trump's decision to abandon the deal", said Mark Dubowitz, CEO of the Foundation for Defense of Democracies, a nonpartisan policy institute.
Several diplomats have said Europe would be ready to discuss sanctioning Iran's ballistic missile tests and forming a strategy to curb Iran's influence in the region.
Iran deal supporters mostly want the U.S.to remain in the agreement because they claim Iran is in compliance and a US withdrawal would alienate America's European allies.
"That's what we have to consider", said Rep. C.A. Dutch Ruppelsburger, D-Md., the former top-ranking Democrat on the House Intelligence Committee. If Trump refuses to certify, Congress will have 60 days to decide whether to re-impose U.S. sanctions on Iran.
Many disagree Iran is in compliance with the JCPOA, including Senators Tom Cotton, R-Ark., Ted Cruz, R-Texas, David Perdue, R-Ga., and Marco Rubio, R-Fla., who spelled out major instances of Iranian noncompliance and cheating in a July 11, 2017 letter to Secretary of State Tillerson.
After de-certification, the U.S. Congress will review - in a process that will take 60 days - whether it is time to re-apply U.S. sanctions on Iran that were suspended after the JCPOA was signed.
The JCPOA has also allowed the worldwide community to make progress in holding Iran accountable for its continued support for terrorism and its many human rights violations, she said.
"At the end of the day, though, everyone recognizes that he's the decider".