By Tom Gillespie and David Mercer, news reporters
Donald Trump has warned Iran that an attack on "anything American" will be met with "great and overwhelming force", with parts of the country facing "obliteration".
The US leader issued the threat as he criticised "ignorant and insulting" remarks by Iran's president, who had earlier mocked Mr Trump by claiming the White House was "afflicted by mental retardation".
Hassan Rouhani said fresh US sanctions imposed on Iran's Supreme Leader Ayatollah Ali Khamenei and his associates were "outrageous and idiotic", amid escalating tensions between the two countries.
In a series of tweets posted on Tuesday, Mr Trump said Iran's "very ignorant and insulting statement… only shows that they do not understand reality".
"Any attack by Iran on anything American will be met with great and overwhelming force," he added.
"In some areas, overwhelming will mean obliteration. No more John Kerry & Obama!"
Mr Trump said Iran's leadership could not comprehend the words "nice or compassion" and only understood "strength and power", with the US "by far the most powerful military force in the world".
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The US president tweeted: "The wonderful Iranian people are suffering, and for no reason at all. Their leadership spends all of its money on terror, and little on anything else."
Iran's foreign ministry has said the latest US sanctions could spell a "permanent closure" to diplomacy between the two countries after Tehran shot down an unmanned American drone last week.
Mr Trump initially told reporters the sanctions were in response to the attack on the aircraft, but later claimed they would have been imposed regardless of the incident.
Russia has said it would counteract the sanctions on Tehran, which it has branded "illegal", and called for dialogue between the US and Iran.
Moscow has also supported Iran's claim that the drone was in Iranian airspace when it was downed and said that US evidence alleging Tehran was behind attacks on American ships in the Gulf of Oman was poor quality and unprofessional.
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