The president says the US can't abide by an agreement if Iran continues destabilizing activities.
Speaking on Wednesday morning in NY, the Iranian President said his regime strives "to build peace and promote the human rights of people and nations". The trade-off - new sanctions in exchange for an unfettered Iranian nuclear program - is undoubtedly worse for USA security.
"An option may be to start enrichment", he said, "not building an atom bomb".
The Iranian president, for his part, said the JCPOA proved that the complicated worldwide disputes could be resolved through dialogue with a win-win approach.
The warning from Trump came in a message to the United Nations agency's annual meeting, being held in Vienna, that was read by U.S. Energy Secretary Rick Perry.
It wasn't clear if Trump had made a final decision to leave or stick with the Iran deal.
When asked if he planned to back out to the deal he has said is an "embarrassment to the United States", Trump told reporters, "I have decided".
Trump has been sharply critical of the nuclear deal and has broadly hinted that his administration would withdraw from the agreement.
"An American government that chooses to trample on her legal and legitimate worldwide commitments, a conversation with such a government would be a waste of time", he said. In his U.N.G.A. speech, Trump reiterated this sentiment, framing his comments on Iran by pitting the people against the government.
Macron, like Trump appearing for the first time at the annual United Nations gathering of world leaders, met his USA counterpart on Monday for their latest meeting - which appeared to be friendly, but did not bridge differences.
TILLERSON: As a long-time negotiator, I learned to never say never.
Aside from the United States, the other signatories have signaled support for keeping the deal, even if European capitals share Washington's concerns about Iran's subversive activities in the Middle East. Accordingly, they say no changes are needed, just continued careful enforcement of the deal's provisions including the IAEA's monitoring of Iran.
Mr Trump has been a harsh critic of the United Nations, but with world leaders and foreign ministers, including Australia's Julie Bishop, looking on inside the UN's packed Economic and Social Council Chamber the president did soften his words.
Asked whether the agreement could survive without the USA, he said "it's a bit early or premature to hold discussions about such questions", adding that the "Europeans want to preserve it".
The US President called the Iranian regime a "corrupt dictatorship" that had turned the country into an "economically depleted rogue state whose chief exports are violence, bloodshed, and chaos". Mogherini declined to say whether Tillerson had pledged to remain committed to the deal, but said the European Union is committed to preserving it.
"The main message is: make the United Nations great - not again", Mr Trump said on Monday.
"So whomever brings their armies to our region, whomever sparks war in our region, whomever has formed and supported terrorist groups in our region is in no position to levy such accusations against the Islamic Republic of Iran", Rouhani said.