A furious President Donald Trump on Monday warned his Iranian counterpart that Tehran risked consequences the likes of which few throughout history have suffered before if he threatens the US again, hours after Hassan Rouhani cautioned that America’s hostile threats may trigger “the mother of all wars.”

The tirade at the highest level signalled an immediate escalation of tensions between Washington and Tehran, weeks after the US left a landmark deal signed in 2015 which curbed Iran’s nuclear activities in return for the lifting of international sanctions.

Rouhani had also warned Trump to stop “playing with the lion’s tail” and threatening Iran, “or else you will regret it.”

In the nearly all-caps tweet, Trump mentioned about the dangers to Iran of making hostile threats after Rouhani said, “America must understand well that peace with Iran is the mother of all peace and war with Iran is the mother of all wars.”

“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,” Trump tweeted, adding that “WE ARE NO LONGER A COUNTRY THAT WILL STAND FOR YOUR DEMENTED WORDS OF VIOLENCE & DEATH. BE CAUTIOUS!”

Even before Trump’s angry tweets, his administration had already intensified the rhetoric against Iran.

In a blistering speech hours earlier, US Secretary of State Mike Pompeo likened the Iranian regime to the mafia, accusing the clerics that rule the country of enriching themselves and funding terrorism at the expense of ordinary Iranians.

“To the regime, prosperity, security, and freedom for the Iranian people are acceptable casualties in the march to fulfill the Revolution,” Pompeo said in remarks delivered at the Ronald Reagan National Library in Simi Valley, California.

“The level of corruption and wealth among regime leaders shows that Iran is run by something that resembles the mafia more than a government,” Pompeo said.

Among the most startling allegations leveled by Pompeo, who was CIA director before becoming secretary of state, was that Iranian Supreme Leader Ali Khamenei has a personal hedge fund worth USD 95 billion, CNN reported.

“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.

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.”

In May, Trump called the nuclear accord – or the Joint Comprehensive Plan of Action (JCPOA), a “horrible, one-sided deal that should have never, ever been made”. The other signatories to the deal – China, France, Germany, European Union, Iran, Russia, United Kingdom – have vowed to stand by it.

Trump has alleged that the deal did not restrict Iran’s “destabilising activities” in the region enough, and could not detect or prevent any breaking of its terms.

The had agreement forced Iran to curtail its uranium enrichment capacity to prevent it developing nuclear weapons, and imposed stringent verification processes, in exchange for relief on crippling sanctions.

Iran insists its nuclear programme is entirely peaceful, and its compliance with the deal has been verified by the International Atomic Energy Agency (IAEA), which has said Iran is honouring its commitments.

Pompeo, in his speech, also said he wanted to try to stop countries importing Iranian oil by November as part of stepping up pressure on Tehran.

In May, he had outlined 12 conditions for any “new deal” between Washington and Tehran, including the withdrawal of its forces from Syria and an end to its support for rebels in Yemen.

The US Treasury has said there will be wind-down periods of 90 and 180 days before sanctions are implemented.

The first deadline, on August 6, will affect the purchase of US dollars, trade in gold and certain other metals, as well as aviation and the car industry.

The next, on November 4, will target Iran’s financial and oil institutions.

Iran is one of the world’s largest oil producers, with exports worth billions of dollars each year.