President Donald Trump escalated a war of words with Iranian counterpart Hassan Rouhani with a menacing tweet late Sunday.

In the nearly all-caps tweet, Trump directly warned the Iranian president to “NEVER, EVER THREATEN THE UNITED STATES AGAIN,” adding that any new ones would bring "CONSEQUENCES THE LIKES OF WHICH FEW THROUGHOUT HISTORY HAVE EVER SUFFERED BEFORE.”

Trump's tweet came hours after Rouhani’s own warning over the weekend, reported by Iranian state news agency IRNA, that Trump was playing “with the lion's tail.”

"America should know that peace with Iran is the mother of all peace, and war with Iran is the mother of all wars," Rouhani said.

Trump called the comments “DEMENTED WORDS OF VIOLENCE & DEATH. BE CAUTIOUS!"

To Iranian President Rouhani: NEVER, EVER THREATEN THE UNITED STATES AGAIN OR YOU WILL SUFFER CONSEQUENCES THE LIKES OF WHICH FEW THROUGHOUT HISTORY HAVE EVER SUFFERED BEFORE. WE ARE NO LONGER A COUNTRY THAT WILL STAND FOR YOUR DEMENTED WORDS OF VIOLENCE & DEATH. BE CAUTIOUS! — Donald J. Trump (@realDonaldTrump) July 23, 2018

He stood by his forceful remarks Monday, when reporter asked if he was concerned about provoking tensions with Iran on Monday.

"Not at all," Trump said during an event at the White House.

The fiery rhetoric by both presidents comes against the backdrop of increasingly adversarial actions between the two nations.

In May, Trump announced his intention to withdraw the U.S. from the Iran nuclear deal and threatened the “highest level” of sanctions against the country and any others that do business with it. Iranian hackers, meanwhile, were planning extensive cyberattacks on U.S. and European targets, prompting consideration of a U.S. counterattack, multiple senior U.S. officials told NBC News.

The Trump administration appears to have launched a concerted verbal assault on Iran.

Speaking in California on Sunday night, Secretary of State Mike Pompeo said the U.S. supports Iranian protesters who he said have been taking to the streets recently to oppose corruption and call for expanded rights.

“In light of these protests and 40 years of regime tyranny, I have a message for the people of Iran: the United States hears you. The United States supports you. The United States is with you," Pompeo said according to prepared remarks released in advance of his speech at the Ronald Reagan Presidential Library and Museum in Simi Valley.

He added: "While it is ultimately up to the Iranian people to determine the direction of their country, the United States, in the spirit of our own freedoms, will support the long-ignored voice of the Iranian people."

On Monday, Iranian Foreign Minister Mohammad Javad Zarif seemed to mock Trump's all-caps broadside with a tweet of his own.

"COLOR US UNIMPRESSED: The world heard even harsher bluster a few months ago," he said on Twitter. "And Iranians have heard them — albeit more civilized ones — for 40 yrs. We’ve been around for millennia & seen fall of empires, incl our own, which lasted more than the life of some countries. BE CAUTIOUS!"