US President Donald Trump says he will withdraw the US from an Obama-era nuclear agreement with Iran.
Calling it "decaying and rotten", he said the deal was "an embarrassment" to him "as a citizen".
Going against advice from European allies, he said he would re-impose economic sanctions that were waived when the deal was signed in 2015.
In response, Iran said it was preparing to restart uranium enrichment, a key for making both nuclear energy and weapons.
Iran's President Hassan Rouhani said: "The US has announced that it doesn't respect its commitments.