With Trump ratcheting up his strident language in recent days, Vice President JD Vance offered his own threatening assessment of what may follow, warning Tehran that US forces have tools they "so far haven't decided to use" against the Islamic republic.

Through weeks of conflict, the United States and its ally Israel have leveled Iranian military targets, killed the country's top leadership and devastated parts of the country's infrastructure.

Early Tuesday he issued one of his most glaring threats of the war.

"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 on his Truth Social platform.

Trump did not give details but he has already said the US military could bomb Iran's bridges, power plants and other civilian infrastructure into the "stone age."

Trump has announced a deadline of midnight GMT Tuesday for Iran to end its de facto closing of the Strait of Hormuz, a narrow, strategic waterway used to transport oil and other commodities.

On Monday, he said a temporary ceasefire proposal being circulated was insufficient.

Iran has rejected US pressure, with state media reporting authorities are insisting that instead of just a ceasefire it wants a full end to the war.

On Truth Social, Trump left the door open for a last-hour agreement.

"Now that we have Complete and Total Regime Change, where different, smarter, and less radicalized minds prevail, maybe something revolutionarily wonderful can happen, WHO KNOWS? We will find out tonight," he wrote.

Trump said Monday that starting in Washington late Tuesday evening, US forces would destroy "every bridge in Iran" and cripple "every power plant" in the country -- something that many experts say would be a blatant war crime.

The extent of Trump's saber rattling and provocative language has appalled critics.

"This is an extremely sick person," top US Senate Democrat Chuck Schumer posted on X. "Each Republican who refuses to join us in voting against this wanton war of choice owns every consequence of whatever the hell this is."

Meanwhile Vance, visiting Hungary, delivered an ominous warning even as he told reporters that Washington has "largely accomplished its military objectives," and that more negotiations were expected ahead of the deadline.

"They've got to know we've got tools in our toolkit that we so far haven't decided to use," Vance said. Trump "will decide to use them if the Iranians don't change their course of conduct."

US and Israeli warplanes have been continuously bombing Iran since February 28, and on Tuesday Tehran said that its crucial oil export terminal on Kharg island was under attack.