US President Donald Trump has struck a blow against the 2015 Iran nuclear agreement in defiance of other world powers, choosing not to certify that Tehran is complying with the deal in a major reversal of US policy.
Mr Trump made the announcement on Friday in a speech that detailed a more confrontational approach to Iran over its nuclear and ballistic missile programs and its support for extremist groups in the Middle East.
"Today I am announcing our strategy along with several major steps we're taking to confront the Iranian regime's hostile actions and to ensure that Iran never - and I mean never - acquires a nuclear weapon," Mr Trump said.
Mr Trump did not pull the US out of the agreement, aimed at preventing Iran from developing a nuclear bomb, but he gave the US Congress 60 days to decide whether to reimpose economic sanctions on Tehran that were lifted under the pact.
That would increase tension with Iran as well as put Washington at odds with other signatories of the accord such as Britain, France, Germany, Russia, China and the European Union.
Iran said it will remain committed to the multinational nuclear deal as long at it serves the country's national interests, and its ballistic missile program will expand despite pressure from the US.
Iranian President Hassan Rouhani said in a live televison address Mr Trump's speech was full of "insults and fake accusations" against Iranian.
"The Iranian nation has not and will never bow to any foreign pressure.... Iran and the deal are stronger than ever.... Iran's Islamic Revolutionary Guards Corps will continue its fight against regional terrorists," Rouhani said.
He added that Mr Trump's decision to decertify the deal would isolate the US as other signatories of the accord remained committed to it. The deal was not renegotiable, he said.
US senator Robert Menendez, one of the Democrats most strongly opposed to the 2015 nuclear agreement with Iran, rejected Mr Trump's plan not to certify Iran's compliance with the international accord.
"Not certifying now does nothing but create uncertainty among our allies and embolden an already belligerent Iran," Mr Menendez said in a statement, adding that the international community should strengthen oversight and enforcement of the nuclear agreement.