US President Donald Trump struck a blow against the 2015 Iran nuclear agreement on Friday in defiance of other world powers, choosing not to certify that Tehran is complying with the deal and warning he might ultimately terminate it.

Trump announced the major shift in US policy in a speech in which he detailed a more aggressive approach to Iran over its nuclear and ballistic missile programs and its support for extremist groups in the Middle East.

US President Donald Trump speaks about Iran and the Iran nuclear deal in front of a portrait of President George Washington in the Diplomatic Room of the White House in Washington, US, October 13, 2017. /Reuters Photo

He singled out Iran’s Islamic Revolutionary Guard Corps for sanctions and delivered a blistering critique of Tehran, which he accused of destabilizing actions in Syria, Yemen and Iraq.

"Iranian dictatorship, its sponsorship of terrorism, and its continuing aggression in the Middle East and all around the world," he said

He also accused Iran of “not living up to the spirit” of the nuclear agreement and said his goal is to ensure Tehran never obtains a nuclear weapon, in effect throwing the fate of the deal to Republican-controlled Congress.

The US president also threatened to rip up the 2015 agreement curbing Iran's nuclear program. "It is under continuous review and our participation can be canceled by me as president at any time," he warned.

US President Donald Trump walks from the Diplomatic Reception Room after speaking about the Iran nuclear deal at the White House in Washington, US, October 13, 2017. /Reuters Photo

Trump said he supports efforts in Congress to work on new measures to address these threats without immediately torpedoing the broader deal.

"We encourage the US administration and Congress to consider the implications to the security of the US and its allies before taking any steps that might undermine" the deal.

Responding to Trump, Iranian President Hassan Rouhani said on Friday on television that Tehran was committed to the deal and accused Trump of making baseless accusations.

“The Iranian nation has not and will never bow to any foreign pressure,” he said. “Iran and the deal are stronger than ever.”

The US's European allies have warned of a split with the United States over the nuclear agreement and say that putting it in limbo as Trump has done undermines US credibility abroad, especially as international inspectors say Iran is in compliance with the accord.

A man watches a television broadcast of US President Donald Trump's speech, in Tehran, Iran October 13, 2017. /Reuters Photo

"We cannot afford as the international community to dismantle a nuclear agreement that is working," Federica Mogherini, the foreign policy chief of the European Union said on Friday, just minutes after Trump's announcement.

She told reporters Trump doesn't have power to cancel the deal and added, "The international community, and the European Union with it, has clearly indicated that the deal is, and will, continue to be in place."

Secretary of State Rex Tillerson responded "to our friends and allies in Europe" by saying: "I think we have a real opportunity to address all the threats that are posed by Iran."

The chief of the UN atomic watchdog reiterated that Iran was under the world’s “most robust nuclear verification regime.”

“The nuclear-related commitments undertaken by Iran under the JCPOA are being implemented,” Yukiya Amano, director general of the International Atomic Energy Agency said, referring to the deal by its formal name.