“A whole civilisation will die tonight, never to be brought back again. I don’t want that to happen, but it probably will,” Trump wrote online early on Tuesday, ahead of the 8 pm ET (2400 GMT) deadline he set for Iran to strike a deal with the US.

At 6:32 pm ET, Trump announced he had agreed to a two-week ceasefire with Iran.

By then, Trump’s threat had drawn harsh criticism from around the globe. Democratic lawmakers in Congress called the president “completely unhinged,” and Iran’s UN ambassador called Trump’s threat “deeply irresponsible” ​and “profoundly alarming.” Pope Leo said threats against the population of Iran are “unacceptable.”

Some of Trump’s fellow Republicans, including former US Representative and one-time staunch Trump ally Marjorie Taylor Greene, openly expressed concern as well, ​though many others defended his approach.

“It’s about time we had a President willing to defend Americans,” the Senate Republican Conference said in a social media post.

Inside the ⁠White House, two officials who spoke on the condition of anonymity to discuss internal matters said Trump’s incendiary rhetoric was generally seen as a negotiation tactic, not an indication that he plans to annihilate Iran or ​use nuclear weapons.

“He’s creating leverage through unpredictability,” one of the officials said. “He wants Tehran to blink.”

The official said several White House aides helped craft the Tuesday morning social media post, but the language about ending a civilisation ​came from Trump himself.

Trump’s demands

Trump has demanded that Iran reopen the Strait of Hormuz, a critical global shipping lane closed by Iran in response to US-Israeli strikes, as well as end support for militant proxies throughout the Middle East. Unless Iran complies, Trump has warned that US forces would attack Iran’s bridges and power plants.

A second White House official noted some unease around the high-stakes deadline. Both officials said the president could follow through on his threats to hit Iranian bridges and power plants, which some international ​law experts and world leaders have criticised as potentially illegal attacks on what is mainly civilian infrastructure.

“As President Trump has said, Iran can never have a nuclear weapon, and the Iranian people welcome the sound of ​bombs because it means their oppressors are losing,” White House spokeswoman Anna Kelly said. “Greater destruction can be avoided if the regime understands the seriousness of this moment and makes a deal with the United States.”

Trump, in his post on Tuesday evening, ‌said the ceasefire ⁠deal was subject to Iran’s agreement to pause its blockade of oil and gas supplies through the strait.

Escalating rhetoric

US Senate Democratic leaders said in a Tuesday statement that it is “unconscionable” for the president to threaten the end of the Iranian civilisation and that such a threat “makes Americans less safe, further destabilises our nation and economy, and puts at greater risk US service members.”

Trump initially described the war as a “short-term excursion” aimed at addressing US concerns quickly, citing the need to prevent Iran from possessing a nuclear weapon as a chief goal.

He has more recently vacillated between saying the war is “ahead of schedule” to “we won” while also vowing that he will not stop ​until Iran is “decisively defeated.”

His language also has grown increasingly ​aggressive, a reflection of what aides said was ⁠his desire to get the unpopular war over with and the Strait of Hormuz opened at a time of rising gasoline prices, US economic jeopardy and concern about whether Republicans can hold onto control of Congress in November elections.

Another person close to the White House said there was “a lot of support” within the West Wing ​for the president’s messaging.

“Staffers are definitely cheering him on,” the person said.

Republican pushback

Trump’s threat against Iranian civilisation has sparked pockets of pushback from within his own ​party.

US Senator Lisa Murkowski of Alaska, ⁠a frequent Trump critic despite being a Republican, said in a social media post that Trump and Iran “must de-escalate their unprecedented sabre-rattling before it is too late.”

Some of the loudest media voices with influence in the president’s base, including right-wing commentator Tucker Carlson, have spoken out against Trump’s rhetoric.

Carlson on Monday called the president’s rhetoric toward Iran, including an expletive-filled threat on Easter, “vile” on “every level.”

Greene, a Georgia Republican who once was one of Trump’s most vocal defenders, suggested ⁠potentially invoking the ​25th Amendment of the US Constitution. That amendment allows the vice president and members of the Cabinet to try to declare ​that a president is unable to discharge the duties of his office.

That part of the amendment has never been invoked and would require majorities of support in Congress, an unlikely scenario with Republicans holding control of both chambers.

“Not a single bomb has dropped on America. We ​cannot kill an entire civilisation,” Greene said in a social media post, adding, “This is evil and madness.”