Trump's move risks overturning years of diplomacy, worsening instability in the Middle East and threatens foreign companies' business in Iran worth billions of dollars.

"The risks of confrontation are real," warned France's Foreign Minister Jean-Yves Le Drian, adding Europe would act to "avoid the explosion (of conflict) that risks happening if... no measures are taken."

Iran reacted furiously to Trump's decision, with lawmakers burning a US flag and chanting "Death to America" in the Iranian parliament. But its regional rivals Saudi Arabia and Israel applauded the US move.

- Protecting business in Iran -

European powers and key trading power China vowed to save the accord and protect companies operating in the country.

Trump's advisor John Bolton said earlier that European firms doing business in Iran now have a six month deadline to wind up investments or risk US sanctions.

European governments are going "to do everything to protect the interests" of their companies, said an official in the French presidency, who asked not to be named.

But Iran's supreme leader Ayatollah Ali Khamenei said Iran too would quit the nuclear deal unless Europeans offered solid guarantees that trade relations would continue.

"If you don't succeed in obtaining a definitive guarantee -- and I really doubt that you can -- at that moment, we cannot continue like this," he told Iran's government in a televised speech.

Chinese foreign ministry spokesman Geng Shuang said China will maintain "normal economic and trade exchanges" with Iran despite Trump's decision.

Beijing will "remain in dialogue with all parties and continue to devote itself to safeguard and implement the deal," he said.

- 'Economic policeman' -

Slapping aside more than a decade and a half of diplomacy by Britain, China, France, Germany, Iran, Russia and past US administrations, Trump called for a "new and lasting deal".

Trump described the 2015 accord as an "embarrassment" to the US that did nothing to contain Iran's nuclear ambitions.

In response, the foreign ministers of France, Britain and Germany will meet Iranian representatives next Monday "to consider the entire situation," Le Drian told RTL radio.

French President Emmanuel Macron will also speak with his Iranian counterpart Hassan Rouhani by telephone on Wednesday afternoon about "our wish to stay in the agreement," Le Drian said.

In separate comments, French Economy Minister Bruno Le Maire said that it was "not acceptable" for the US to be the "economic policeman of the planet".

- 'Bomb threat' -

Trump said a deal with Iran would have to include not just deeper restrictions on its nuclear programme, but on its ballistic missiles and support for militant groups across the Middle East.

"We will not allow American cities to be threatened with destruction," he said.

"We will not allow a regime that chants 'Death to America' to gain access to the most deadly weapons on Earth."

Iranian President Rouhani said Iran could resume uranium enrichment "without limit" in response to Trump's announcement.

But he said Iran would discuss its response with other parties to the deal before announcing a decision.

Trump warned: "If the regime continues its nuclear aspirations, it will have bigger problems than it has ever had before."

- Blow for Europe -

The decision marked a stark diplomatic defeat for Europe, whose leaders begged the US leader to think again.

In a joint statement, Germany's Angela Merkel, Britain's Theresa May and France's Macron voiced their "regret and concern" at Trump's decision.

Bolton insisted that cooperation with Europe on Iran was not over.

The US will "work with the Europeans and others not only on the nuclear issue but on Iran's ballistic missile development, its continuing support for terrorism and its military activities that jeopardise our friends," he told Fox News.

- 'Bold decision' -

Trump's decision offers him a domestic political victory, fulfilling a longstanding campaign promise.

But the long term impact for US foreign policy and for the Middle East was less clear.

Turkish President Recep Tayyip Erdogan on Wednesday said that the United States will "lose in the end" from its decision.

Israeli Prime Minister Benjamin Netanyahu strongly supported the move.

Saudi Arabia's foreign ministry said it supported Trump's move and the sanctions. It said it will take all necessary measures to prevent oil supply shortages following the move. Like Saudi Arabia, Iran is a major crude producer.

Some analysts also warned the move would complicate US efforts to reach an agreement with North Korean leader Kim Jong Un over his country's own more advanced weapons programme.

Former CIA director John Brennan said Trump's move "gave North Korea more reason to keep its nukes".

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RTL GROUP