European powers say they are committed to the Iran nuclear deal, after President Donald Trump announced the US was withdrawing from the agreement.
The UK, France and Germany urged the US not to obstruct its implementation.
They said they would work with the other signatories to the 2015 deal – Russia and China – which have stressed continuing support for the accord.
In response, Iran said it would restart uranium enrichment, if the agreement could not be salvaged.
In a statement, President Hassan Rouhani said: “I have ordered the foreign ministry to negotiate with the European countries, China and Russia in the coming weeks.
“If we achieve the deal’s goals in co-operation with other members of the deal, it will remain in place.”
There were furious scenes in the Iranian parliament, with members burning an American flag and the speaker reportedly saying Mr Trump lacked “mental capacity”.
In a televised address on Tuesday, President Donald Trump said the US would withdraw from the JCPOA. He called it a “horrible, one-sided deal that should have never, ever been made”.
Rather than protecting the US and its allies, he said it had placed “very weak limits on the regime’s nuclear activity and no limits at all on its other malign behaviour, including its sinister activities in Syria, Yemen and other places”.
The president added that the accord did not deal with Iran’s development of ballistic missiles, and that its inspections mechanisms were not strong enough.
He said he would reimpose economic sanctions that were waived when the deal was signed in 2015.
The US Treasury said the sanctions would target industries mentioned in the deal, including Iran’s oil sector, aircraft manufacturers exporting to Iran and Iranian government attempts to buy US dollar banknotes.
US National Security Adviser John Bolton is reported as saying that European companies doing business in Iran will have to stop doing so within six months or face US sanctions.
The deal was not perfect. It did not cover a range of worrying Iranian activities from its missile programme to its regional behaviour.
The inconvenient truth for Donald Trump is that, as far as it goes, the nuclear deal was working.
Despite this, Mr Trump presented it in stark and frankly erroneous terms – for leaving out things that it was never supposed to cover in the first place.
He has put US diplomacy on a collision course with some of Washington’s closest allies.
And some fear that he may have brought a new and catastrophic regional war in the Middle East that much closer.