Trump’s warning regarding a nuclear deal on Wednesday came after he had promised Washington would intervene to help those involved in a brutal crackdown on protests in the country earlier this month.
He had said help was “on the way”, before saying he had been told the execution of demonstrators had stopped.
On Thursday, he said he had told Iran that it had to do two things to avoid military action: “Number one, no nuclear. And number two, stop killing protesters.”
The US-based Human Rights Activists News Agency (HRANA) said it had confirmed the killing of more than 6,300 people, including more than 5,900 protesters, since the unrest began at the end of December.
It said it was also investigating another 17,000 reported deaths received despite an internet shutdown after nearly three weeks.
Another group, the Norway-based Iran Human Rights (IHR), has warned the final toll could exceed 25,000.