Almost a year on, Trump has met Kim - who he once called "Rocket Man" on a "suicide mission" - for a landmark summit in Singapore, and follow-up talks are underway between the two sides.
The tweet was reverberating across the Mideast.
Tension between the US and Iran has been high ever since Trump pulled out of the United States' 2015 nuclear deal with Iran.
While one can't fault the President for sticking up for this nation, most political pundits will likely see this as yet another overreaction and misuse of Twitter in a way which literally could spark a nuclear war in the Middle East.
Rouhani's tough talk is directly connected with the economic turmoil there, according to the Lowy Institute's Rodger Shanahan.
The Iranian president also scoffed at his American counterpart's threat to halt Iranian oil exports saying the country has a dominant position in the Gulf and the Strait of Hormuz. The 2015 agreement was in response to fears that Iran was developing a nuclear bomb. While the media and Democrats used this tweet to suggest Trump was unhinged and unsafe, this response was far from unprovoked. "BE CAUTIOUS!", he wrote.
Others simply rewrote President Trump's tweet with song lyrics.
He cited the harsh words between the USA and North Korea that preceded the high profile summit between Trump and North Korean leader Kim Jong Un and denuclearization talks. North's Foreign Ministry accused the United States of making "gangster-like" demands for its unilateral disarmament.
Camera IconUS Secretary of State Mike
Iran has faced increased USA pressure and possible sanctions since May.
The conflict between Iran and the US traces back to the 1979 Islamic Revolution, but Obama attempted to paper over the country's problems with the Iran deal.
He said the war of words between the two presidents was to be expected, since official diplomatic relations between the two countries have been frozen for decades.
Top Cabinet officials have recently said countries could get sanctions relief on a case-by-case basis if they cannot entirely cut off purchases from Iran by November.
Pompeo added: "The level of corruption and wealth among regime leaders shows that Iran is run by something that resembles the mafia more than a government".
Among the most startling allegations leveled by Pompeo, who was Central Intelligence Agency director before becoming secretary of state, was that Iranian Supreme Leader Ali Khamenei has a personal hedge fund worth $95 billion. He also said the government has "heartlessly repressed its own people's human rights, dignity and fundamental freedoms".
Pompeo said that the government has become a nightmare for the Iranian people.
Rouhani's message came amid rising tensions between his country and the United States.
Multiple people shot in Toronto's Riverdale neighbourhood, paramedics say
Nearby streets have been closed and the Toronto Transit Commision said trains were not stopping in the area. A number of people are believed to have been shot, several fatally, in front of a bar in Toronto.