Trump had asked the National Security Council to prepare in the Situation Room for his return from the G7 summit in Canada.
Earlier, the White House announced that Trump intends to leave the G7 summit in Canada due to developments in the Middle East.
Trump's directive to the National Security Council to prepare came about two hours after he tweeted on Truth Social, warning everyone in Tehran to "evacuate immediately," as the military confrontation between Iran and Israel escalated.
Trump tweeted: "Iran should have signed the deal I asked them to sign."
"What a disgrace, what a waste of human life. Iran simply cannot possess a nuclear weapon," he continued, adding, "Everyone must evacuate Tehran immediately."
The White House's Twitter page retweeted Trump's tweet, confirming the warning, which calls for the immediate evacuation of Tehran.
"I don't want a nuclear weapon in Iran."
In another post, Trump said, "America First means many great things, including that Iran can never have a nuclear weapon," concluding, "Make America Great Again."
On Monday, the US Department of Defense (Pentagon) announced that it had directed the aircraft carrier USS Nimitz from the South China Sea to the Middle East.
Earlier, during his meeting with Canadian Prime Minister Mark Carney on the sidelines of the first day of the G7 leaders' summit in Alberta, Canada, Trump said that Iran must return to the negotiating table.
He added that Iran wants to negotiate, but that it has been too late, and that what is happening is painful for both sides. He stressed that "Iran will not win this war and must return to the negotiating table before it is too late."
Following his meeting with British Prime Minister Keir Starmer on Monday on the sidelines of the summit, the US president said, "I don't want to see a nuclear weapon in Iran, and we are taking the necessary steps to ensure that doesn't happen."
He claimed that he had given Iran "a 60-day deadline to return to the nuclear negotiating table, but Tehran did not respond during that period."
Trump expressed confidence that Iran would return to the negotiating table, adding, "I think Iran wants to make a nuclear deal. It would be foolish not to sign it. They should have signed the deal."
On Friday, Israel—with US support—launched a massive attack on Iran, bombing nuclear facilities and missile bases and assassinating military leaders and nuclear scientists, leaving a total of 224 dead and 1,277 wounded.
On the same day, Iran began responding with ballistic missile and drone attacks, which also caused significant material damage, 24 deaths, and 592 injuries, according to the Israeli Government Information Office.
Tel Aviv and Tehran are mutually hostile, and Israel's current aggression against Iran is the most extensive, representing a transition from a "shadow war" of bombings and assassinations to an open military conflict.
