Iran condemned Donald Trump on Sunday as a "terrorist in a suit" after the US president threatened to hit 52 Iranian sites hard if Tehran attacks Americans or US assets in retaliation for the killing of military commander Qassem Soleimani.
As the two countries assailed each other in a war of words, the European Union, Britain and Oman urged both to make efforts to defuse the crisis.
Soleimani, Iran's pre-eminent military commander, was killed on Friday in a US drone strike on his convoy at Baghdad airport, an attack that took long-running hostilities between Washington and Tehran into uncharted territory and raised the spectre of wider conflict in the Middle East.
Heightened fears of war drove Gulf stocks sharply lower on Sunday. Hundreds of thousands of mourners, many chanting, beating their chests and wailing in grief, turned out across Iran to show their respects after Soleimani's body was returned home to a hero's welcome.
Information and Telecommunications Minister Mohammad Javad Azari-Jahromi tweeted:
Like ISIS, Like Hitler, Like Genghis! They all hate cultures. Trump is a terrorist in a suit. He will learn history very soon that NOBODY can defeat 'the Great Iranian Nation & Culture'
Soleimani was the architect of Tehran's military operations abroad as head of the Revolutionary Guards' Quds Force. Supreme Leader Ayatollah Ali Khamenei promised on Friday that Iran would seek harsh revenge for his death.
US Secretary of State Mike Pompeo said that if there were further Iranian attacks on US targets, Washington would respond with lawful strikes against decision-makers orchestrating such attacks. Democratic critics of the Republican president have said the strike that Trump authorised was reckless and risked more bloodshed in a dangerous region.
Iranian Supreme Leader Ali Khamenei, who gave Soleimani the country's highest honor last year, vowed "severe retaliation" in response to his killing. Thousands mourned his death in Iraq, Iran and Gaza.
Qassem Soleimani was the head of Iran's elite Quds Force and the mastermind of its regional security strategy. He was killed early Friday near the Baghdad international airport along with senior Iraqi militants in an airstrike ordered by President Donald Trump. The attack has caused regional tensions to soar and tested the US alliance with Iraq. Fearing escalation, NATO has suspended it's training activities in Iraq, while the British Navy has committed to escort every UK-flagged ship across the Straits of Hormuz.
Showing no signs of seeking to reduce tensions, the US president has since issued a stern threat to Iran on Twitter, saying that the US has targeted 52 Iranian sites that it would strike if Iran attacks Americans or US assets in response to the US drone strike that killed Soleimani. He later added that the US will use 'new' equipment to strike Iran.