Donald Trump has upped the ante in his social media war of words with Iran.
It comes after Iran's most powerful military commander, General Qasem Soleimani, was killed by a US drone strike in Iraq.
The 62-year-old led military operations for Iran in the Middle East as head of the elite Quds Force, which the US president regarded as an "international terrorist organisation".
He was killed on Friday at Baghdad International Airport along with other militia figures, with at least four others thought to have been killed.
It emerged that the strike had been ordered by US president Donald Trump and it signalled an escalation in tensions between Washington and Tehran.
On Friday, he tweeted: "Iran never won a war, but never lost a negotiation!"
The Supreme Leader of Iran, Ayatollah Ali Khamenei warned that "severe revenge awaits the criminals" who were behind the attack. He announced three days of national mourning.
The Quds Force reported directly to the Ayatollah and he was regarded as a heroic national figure in Iran.
President Trump, who is in Florida, had previously tweeted a symbolic image of the American national flag as news of the attack broke.
A statement from the Pentagon said Soleimani had been "developing plans to attack American diplomats and service members in Iraq and throughout the region".
Protest have been held in Iran as people wept to publicly mourn the dead general.
It was aimed at deterring future Iranian attack plans.
Global oil prices increased by more than 4 per cent in the aftermath of the drone strike.
Mr Trump faced ridicule after a 2011 video surfaced in which he claimed the then President, Barack Obama, was seeking conflict with Iran for domestic political advantage.
He tweeted on November 29, 2011: "In order to get elected, @BarackObama will start a war with Iran".
Eleven months later, on October 9, 2012, he tweeted: "Now that Obama's poll numbers are tailspin - watch for him to launch a strike in Libya or Iran. He is desperate."
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