United States President Donald Trump on Tuesday announced the US withdrawal from what he called the “defective” multinational nuclear deal with Iran, and said Washington would reinstate sanctions against the Islamic republic.

“The Iran deal is defective at its core,” Trump said in a televised address from the White House. “I am announcing today that the United States will withdraw from the Iran nuclear deal.”

He called Tehran the world's leading state sponsor of terror, and decried its influence in the Middle East.

After consulting US “friends” from across the Middle East, Trump said, “it is clear to me that we cannot prevent an Iranian nuclear bomb under the decaying and rotten structure of the current agreement.”

“America will not be held hostage to nuclear blackmail,” Trump vowed.

“We will be instituting the highest level of economic sanction,” Trump said. “Any nation that helps Iran in its quest for nuclear weapons could also be strongly sanctioned by the United States.”

National Security Adviser John Bolton told reporters after Trump's speech that the US sanctions would apply to new contracts “immediately,” and that foreign firms would have months to wind down existing operations in Iran.

Iran could resume uranium enrichment 'without limit': Rouhani

President Hassan Rouhani said Iran could resume uranium enrichment “without limit” in response to Trump's decision.

“I have instructed the Iranian Atomic Energy Organisation to take the necessary measures for future actions so that if necessary we can resume industrial enrichment without limit,” he said on state television.

“We will wait several weeks before applying this decision. We will speak with our friends and allies, the other members of the nuclear agreement,” he said.

'France, Germany, Britain 'regret' Trump's decision'

French President Emmanuel Macron said France, Germany, and Britain regretted US President Donald Trump's decision to withdraw from the 2015 Iran nuclear deal.

“France, Germany, and the UK regret the US decision to leave the JCPOA (Iran deal). The nuclear non-proliferation regime is at stake,” he wrote on Twitter.

“We will work collectively on a broader framework, covering nuclear activity, the post-2025 period, ballistic activity, and stability in the Middle-East, notably Syria, Yemen, and Iraq,” he added.

Pompeo heading to Pyongyang to prepare summit

Trump further announced that Washington's chief diplomat Mike Pompeo is on his way to North Korea to prepare for a landmark nuclear summit.

“At this very moment, Secretary Pompeo is on his way to North Korea in preparation for my upcoming meeting with Kim Jong Un,” Trump said, in a White House address.

Pompeo, who met Kim in Pyongyang last month while he was still director of the CIA, will arrive in the North in “virtually an hour,” Trump said.

In addition to planning the summit, due later this month or early in June, Pompeo has been pressing the regime to release three detained US citizens.