United States President Donald Trump has reiterated his threats against Iran, as negotiations to end the conflict between the two countries continue to flounder.

In a Sunday morning post on his platform Truth Social, Trump warned that time was running short before a fresh wave of US military action might be launched.

“For Iran, the Clock is Ticking, and they better get moving, FAST, or there won’t be anything left of them,” Trump wrote in the short, two-sentence message. “TIME IS OF THE ESSENCE!”

The post was the latest example of Trump using violent rhetoric against Iran as his administration struggles to achieve its goals in the war.

Just a day earlier, Trump had posted an AI-generated image of himself atop a military ship, labelled, “It was the calm before the storm.”

The conflict began on February 28, when Israel and the US jointly attacked Iran.

Since then, Trump has put forward a range of objectives for the resulting war, including dismantling Iran’s missile arsenal, severing its relations with regional allies, and ending its nuclear enrichment programme.

On April 7, Trump coupled those demands with a social media post suggesting wholesale destruction in Iran. Critics have likened the post to a call for genocide.

“A whole civilization will die tonight, never to be brought back again. I don’t want that to happen, but it probably will,” Trump wrote.

Within hours of the post, the US and Iran agreed to a ceasefire that has been in place ever since, though both sides have accused each other of violations.

The US president had previously threatened to attack the country’s civilian infrastructure, including its power plants and bridges, which legal experts warn could amount to a violation of the Geneva Convention.

Separately, in a May interview with Fox News, Trump said Iranian officials will “be blown off the face of the earth” if they attack US vessels.

Iran has denounced such rhetoric and rejected Trump’s demands as excessive.

Mehr, a news agency sponsored by the Iranian government, issued a statement on Sunday saying that the US has offered “no tangible concessions” in its latest proposals.

It also accused the US of seeking to “obtain concessions that it failed to obtain during the war”, a strategy that “will lead to an impasse in the negotiations”.

Separately, a spokesperson for Iran’s armed forces, Abolfazl Shakarchi, was quoted as warning the US against further threats.

“Repeating any folly to compensate for America’s disgrace in the Third Imposed War against Iran will result in nothing but receiving more crushing and severe blows,” he told Mehr.

Reporting from Tehran, Al Jazeera correspondent Almigdad Alruhaid said that the Iranian government has indicated that violent rhetoric from the US will not be tolerated.

“From what we understand, this kind of language is not acceptable here in Tehran. They are projecting defiance rather than [giving] an immediate response to this kind of rhetoric,” Alruhaid said.

He added that the increasingly hostile remarks from both sides signal that the ceasefire could be at imminent risk of shattering.

“Behind all of this rhetoric, there is awareness that the diplomatic window right now is narrowing,” Alruhaid said.

“We do know that there is hard language, hard messaging from both sides — that the finger’s on the trigger on both sides.”

But Adam Clements, a foreign policy analyst, told Al Jazeera there could be a “domestic element” to Trump’s hardline rhetoric, including his latest flurry of messages.

“Of course, Iran would have to take it seriously,” Clements said of Sunday’s post.

“At the same time as well, President Trump is known for his bombastic tweets, his bombastic statements, perhaps for domestic audiences.”

Clements added that it will be critical to watch whether Trump’s statements are echoed by his officials in the coming days, and whether they are also matched by increased military activity.

“ The White House press office has been known to post these type of strange memes, or AI-generated memes and cartoons in the past,” he explained.

“So I think it’s necessary here to sometimes look past some of the political noise, some of the things for show, and really try to pay attention to these clear signals.”