Global powers, including key US allies, have said they will stand by the Iran nuclear deal which US President Donald Trump has threatened to tear apart.
Mr Trump said on Friday that he would stop signing off on the agreement.
The UK, France and Germany responded that the pact was "in our shared national security interest". The EU said it was "not up to any single country to terminate" a "working" deal.
Iran's President Hassan Rouhani said the US was "more isolated than ever".
"Can a president annul a multilateral international treaty on his own?" he asked.
"Apparently he doesn't know that this agreement is not a bilateral agreement solely between Iran and the United States."
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The deal, signed in 2015, is between Iran and six international powers - the UK, the US, Russia, France, Germany, and China. It imposed curbs on Iran's nuclear programme in return for an easing of international sanctions.
In a combative speech on Friday, Mr Trump called Iran a "fanatical regime" and said it had violated the terms of the deal. He accused Iran of sponsoring terrorism, and proposed new sanctions.
"We will not continue down a path whose predictable conclusion is more violence, more terror, and the very real threat of Iran's nuclear breakout," he said.