US President Donald Trump's speech outlining an aggressive new strategy against Iran violated Tehran's nuclear agreement with world powers, said Foreign Minister Mohammad Javad Zarif.
Trump's virulent speech contravened three articles of the 2015 deal, Zarif said in televised remarks broadcast late on Saturday.
They include the requirement to implement the accord "in good faith" and for the US to "refrain from re-introducing or re-imposing" sanctions related to Iran's nuclear programme.
"I have already written nine letters (to EU foreign policy chief Federica Mogherini) listing the cases where the United States has failed to act on or delayed its commitments under the JCPOA," Zarif said, using the technical name for the nuclear deal.
Mogherini helped negotiate the nuclear deal alongside the US, Britain, France, Germany, China and Russia.
Zarif said he would write a new letter regarding Trump's speech last Friday, and warned of a "reciprocal measure" if sanctions were reimposed.
In his speech, Trump refused to "certify" the nuclear deal and warned he would "terminate" the deal unless Congress introduced tough new sanctions against Iran's missile and nuclear programmes, as well as its "destabilising" activities in the Middle East.
Zarif responded by saying: "Our achievements in the field of ballistics are in no way negotiable.
"We live in a region into which hundreds of billions of dollars of lethal American weapons have poured, turning it into a gunpowder storehouse... so we have the right to have defensive means," he said.
Meanwhile, Iran's Atomic Energy Organization chief Ali Akbar Salehi said the country would no longer abide by the Additional Protocol of the Non-Proliferation Treaty if the nuclear deal fell apart.
The protocol allows unannounced inspections by the UN nuclear watchdog, the International Atomic Energy Agency (IAEA). Iran agreed to implement it as part of the nuclear deal, without turning it into law.
"Without the nuclear agreement its application is meaningless," Salehi told state television.
He also repeated his warning that Iran could very quickly return to the production of highly enriched uranium if the US reimposed sanctions.
"If one day, the leaders of the country conclude that the nuclear agreement is no longer to the benefit of the country and decide to resume 20 percent enrichment we can do so within four days," he said.
Weapons-grade uranium is enriched to 90 percent, but most of the work to get there has already been done once scientists have achieved 20 percent.