President Donald Trump on Wednesday warned time is running out for Iran to come to the table and avoid US military action, provoking Tehran to retort that it would respond to any attack "like never before".
Trump has not ruled out an attack after this month's deadly crackdown on protests. Last June, the US carried out a night of strikes on Iranian nuclear sites during Israel's 12-day war against the country.
A US naval strike group that Trump described as an "armada" led by aircraft carrier the USS Abraham Lincoln is now lurking in Middle East waters.
A rights group said that it has verified over 6,200 deaths, mostly of protesters killed by security forces, in the wave of demonstrations that rocked the clerical leadership since late December but peaked on January 8 and 9.
Activists say that the actual toll could be many times higher, with an internet shutdown still complicating efforts to confirm information about the scale of the killings.
In his latest post on Truth Social, Trump did not mention the protests but said Iran needed to negotiate a deal over its nuclear program, which the West believes is aimed at making an atomic bomb.
"Hopefully Iran will quickly 'Come to the Table' and negotiate a fair and equitable deal -- NO NUCLEAR WEAPONS -- one that is good for all parties. Time is running out, it is truly of the essence!" said Trump.
Referring to American strikes against Iranian nuclear targets during the June war which he said resulted in "major destruction of Iran", he added: "The next attack will be far worse! Don't make that happen again".
In response Iran's mission to the United Nations posted a screenshot of Trump's threat on X and wrote: "Iran stands ready for dialogue based on mutual respect and interests -- BUT IF PUSHED, IT WILL DEFEND ITSELF AND RESPOND LIKE NEVER BEFORE!"
Analysts say US options include strikes on military facilities or targeted hits against the leadership under Ali Khamenei, in a full-scale bid to bring down the system that has ruled Iran since the 1979 revolution that ousted the shah.
- 'Severe damage' -
But Foreign Minister Abbas Araghchi said before Trump's comments were published that "conducting diplomacy through military threat cannot be effective or useful".
"If they want negotiations to take shape, they must certainly set aside threats, excessive demands and raising illogical issues," he said in televised comments.
Araghchi said he had "no contact" with US Middle East envoy Steve Witkoff in recent days and that "Iran has not sought negotiations".
Iranian armed forces chief of staff Habibollah Sayyari warned the US against any "miscalculation", saying that "they too would suffer damage".
- 'New dimensions of crackdown' -
In an updated toll, the US-based Human Rights Activists News Agency (HRANA) said it had confirmed that 6,221 people had been killed, including 5,856 protesters, 100 minors, 214 members of the security forces and 49 bystanders.
But the group added it was still investigating another 17,091 possible fatalities. At least 42,324 people have been arrested, it said.
HRANA warned that security forces were searching hospitals for wounded protesters, saying this highlighted "new dimensions of the continued security crackdown".
HRANA said a trial in Malard outside Tehran on Tuesday of a man accused over the death of a police officer was the first such hearing linked to the protests. Images of the hearing were broadcast on state television in Iran.
It was a "starting point for a broad series of trials" that would be "aimed at imposing severe penalties on protesters", HRANA said.
Meanwhile, Iran on Wednesday executed a man arrested last year on charges of spying for Israel's Mossad spy agency, the judiciary said. Rights groups fear some protesters could also face the death penalty.
