US President Donald Trump has launched a blistering all-capitals attack on Iran via Twitter.

In a vicious response to Iranian President Hassan Rouhani, the US leader warned him to "NEVER, EVER THREATEN THE UNITED STATES AGAIN", or he will "SUFFER CONSEQUENCES THE LIKES OF WHICH FEW THROUGHOUT HISTORY HAVE EVER SUFFERED BEFORE".

It came after Rouhani issued a warning to Trump, which was disseminated via the country's state media network.

WHAT WAS THE THREAT?

President Rouhani threatened Trump earlier today, warning that the "mother of all wars" would take place if the US maintained its hostilities.

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"Mr Trump, don't play with the lion's tail, this would only lead to regret," he told a gathering of Iranian diplomats.

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

"You are not in a position to incite the Iranian nation against Iran's security and interests."

WHY TENSIONS ARE BREWING

Trump's withdrawal from nuclear deal

Iran is facing increased US pressure after Trump's decided to withdraw from a nuclear deal.

In 2015, under Barack Obama's administration, Iran agreed to freeze its nuclear program in exchange for the removal of international sanctions.

The West had long held concerns that the Iranian government was developing a nuclear bomb, even though Iran swore its atomic program was for civilian purposes.

After 21 months of negotiations, the deal was signed. It heavily limited Tehran's nuclear capabilities, and their compliance was checked by United Nations inspectors repeatedly.

Trump was wary of the deal and Iran's commitment to freezing its nuclear aims.

He described it "as the worst deal ever made" and an "embarrassment".

Trump's threat to stop oil exports

Rouhani scoffed at Trump's threat to halt Iranian oil exports and said Iran had a dominant position in the Gulf and the Strait of Hormuz, a major oil shipping waterway.

He suggested Iran may block Gulf oil exports if its own trade is disrupted.

Iran's oil exports may fall by as much as two-thirds by the end of the year based on US sanctions, adding new pressure to the already-strained market.

State Department issues anti-Tehran posts

Washington has been accused of pushing online propaganda aimed at stirring up social unrest in Iran.

The State Department's Farsi-language Twitter account and its ShareAmerica website have been frequently critical of Tehran this past month.

Iran is the subject of four of the top five items on the website's "Countering Violent Extremism" section.

They include headlines such as "This Iranian airline helps spread violence and terror".

In social media posts and speeches, Secretary of State Mike Pompeo also appeals directly to Iranians, the Iranian diaspora and a global audience.