Donald Trump has warned Iranian President Hassan Rouhani that he will face dire consequences for threatening the United States.
The US President tweeted early on Monday about the dangers to Iran of making hostile threats after Mr Rouhani said on Sunday "America must understand well that peace with Iran is the mother of all peace and war with Iran is the mother of all wars".
Mr Trump responded with a tweet that warned: "NEVER EVER THREATEN THE UNITED STATES AGAIN OR YOU WILL SUFFER CONSEQUENCES THE LIKE OF WHICH FEW THROUGHOUT HISTORY HAVE EVER SUFFERED BEFORE."
The president earlier this year pulled the United States out of the international deal meant to prevent Tehran from developing a nuclear weapon and ordered increased American sanctions.
Mr Rouhani warned Mr Trump to stop "playing with the lion's tail" and threatening Iran, "or else you will regret it".
The US leader had suggested Iranian leaders are "going to call me and say 'let's make a deal'" but Iran has rejected talks.
Mr Rouhani previously lashed out against Mr Trump for threatening to re-impose the sanctions, as well as for moving the US embassy to Jerusalem and banning travel to the US from certain Muslim-majority countries.
The president's tweet suggested he has little patience with the trading of hostile messages with Iran, using exceptionally strong language and writing an all-capitalised message.
"WE ARE NO LONGER A COUNTRY THAT WILL STAND FOR YOUR DEMENTED WORDS OF VIOLENCE & DEATH. BE CAUTIOUS!," he wrote.
Mr Trump has a history of firing off heated tweets that seem to quickly escalate long-standing disputes with leaders of nations at odds with the US.
In the case of North Korea, the public war of words cooled quickly and gradually led to the high profile summit and denuclearisation talks.