US President Donald Trump has refused to certify Iran's compliance with a landmark 2015 deal curtailing Tehran's nuclear programme in exchange for sanctions relief.
Trump - who opposed the agreement between Iran and world powers, including the US, from the outset - on Friday said that Iran was not living up to the spirit of the accord, despite the UN nuclear watchdog repeatedly confirming that the country was complying with its obligations.
"We cannot and will not certify make this certification," Trump said during a speech from the White House as he laid out an aggressive new strategy towards Iran.
"We will not continue down the path whose predictable conclusion is more violence, more terror and the very real threat of Iran's nuclear breakout," he added.
"That is why I am directing my administration to work closely with Congress and our allies to address the deal's many flaws so that the Iranian regime can never threaten the world with nuclear weapons."
Trump's move does not immediately pull the US out of the deal but pushes action to the Republican-controlled US Congress.
Legislators now have a non-binding 60-day period to debate the accord and decide whether to re-impose sanctions, which would put the deal at risk.
Trump said he wanted Congress to toughen US policy towards Iran, but added that if "we are not able to reach a solution ... then the agreement will be terminated".
Despite the current deal only covering Iran's nuclear activities, Trump said he would ask legislators to find a way to punish Tehran for its ballistic missile programme.
He also accused Iran of destabilising actions in the Middle East, and singled out the Islamic Revolutionary Guard Corps, Iran's main military force, for sanctions.
Al Jazeera's Kimberly Halkett, reporting from Washington, DC, said that Trump had used "a lot of tough talk but not followed up particularly by any immediate action".
She added that Trump's "very strong" speech was "a marked contrast" to comments made to the press by US Secretary of State Rex Tillerson on Thursday evening.
"That was a much more measured approach, one that seemed to imply that there was a desire to work with the US' partners in Europe, and even in the region," Halkett said.
Under 2015's Joint Comprehensive Plan of Action (JCPOA), also signed by Britain, France, Germany, Russia and the European Union, Tehran agreed to restrict its nuclear programme in return for the lifting of most international sanctions that had crippled its economy.
But in the US, opponents of the deal passed legislation requiring the country's president to certify every 90 days that Iran is upholding its part of the agreement.
Trump had already recertified the deal twice since his inauguration in January. But his move on Friday means that Congress can now restore sanctions withdrawn under the 2015 agreement, or introduce new ones within 60 days of the current certification expiring.
The threat of new sanctions has drawn criticism from Iran, which has threatened to withdraw partially or completely from the deal if new penalising measures were imposed.
Iranian officials say the UN's International Atomic Energy Agency (IAEA) is the only authority for verifying Iran's compliance.
Before Trump's speech, Tehran said it would retaliate against any action targeting its armed forces, including the Revolutionary Guards.
"The Iranian government has been very clear that it will not tolerate any change to the nuclear agreement," Al Jazeera's Zein Basravi, reporting from Tehran, said.
"They will not tolerate any sanctions or targeting of its Revolutionary Guard," he added.
US allies, such as the UK and France, had also urged Washington to not jeopardise the deal, with analysts warning Trump's actions could affect his country's standing abroad.
"[Decertifying] would isolate the US from its transatlantic partners," said Matthew Moran, a reader in International Security at King's College London.
"Unilateral action to undermine a multilateral agreement would be very poorly received," he added, continuing: "It would undermine US credibility and discourage other countries from trusting in agreements negotiated with US."
Critics said Trump's actions put international relations at risk and could spell the end of a deal painstakingly negotiated for more than 10 years.
"The deal was working, it was delivering," Trita Parsi, of the National Iranian American Council, told Al Jazeera.
"The Iranians were living up to it - the IAEA certified eight times that Iran was adhering to the deal. Trump took a perfectly working deal and transformed it into a crisis with the decision that he made today."
Congress to decide
By withdrawing his endorsement, Trump has also shifted responsibility for the consequences that stem from potential sanctions on to Congress, according to analysts.
"Congress passed the buck on this in 2015, and now Trump is trying to pass it back," said Steven Hurst, a US foreign policy analyst and academic.
"If ... Congress reimposes sanctions, they take full ownership of the policy and what happens as a result of it. They really won't want to do that, as they didn't in 2015," added Hurst, of Manchester Metropolitan University.
He argued that posturing to voters rather than genuine fears that Iran is contravening its obligations under the deal were influencing the Republican president's behaviour, as well that of many of the party's legislators.
"Certifying that Iran is in compliance goes down terribly with his core voters, and Trump clearly craves their approval," said Hurst.
Congress normally likes to posture on foreign policy issues that resonate with American voters but they rarely actually take responsibility for them by taking concrete actions that might leave them owning the problem
Steven Hurst, Lecturer in American Foreign Policy, Manchester Metropolitan University
Hurst pointed to the example of the Iran Nuclear Agreement Review Act of 2015 to support the idea that most legislators were against rejecting JCPOA.
The law required a two-thirds majority to reject the deal instead of simple majority approval as is normal procedure for such agreements. This "more or less guaranteed that the JCPOA would not be rejected" because such a motion would struggle to draw enough support, Hurst said.
"In essence, Congress normally likes to posture on foreign policy issues that resonate with American voters but they rarely actually take responsibility for them by taking concrete actions that might leave them owning the problem," he said.
Even if the sincerity of Republican opponents to the Iran deal were not in question, Hurst argued that there would likely be enough open opposition in the party to scupper any attempts to sink the agreement.
The Republicans control 240 of 435 seats in the House of Representatives but carry a slender majority of just four in the Senate where they have 52 of 100 seats.
"In the first place, it isn't clear that there will be a majority to support new sanctions, particularly in the Senate," Hurst said, adding that "Trump has done a pretty good job of alienating important members of his own party, notably Senator Bob Corker, one of the key players in the congressional negotiations in 2015".
Hurst added, "it's hard to see Corker voting to reimpose sanctions, and he's unlikely to be on his own".
Sanctions not related to Iran's nuclear programme remain unaffected by Trump's decision.
As recently as last July, the US imposed sanctions on 18 Iranian individuals and entities for supporting what it said was "transnational criminal activity".
Source: Al Jazeera News