A red flag has been raised during a ceremony to honour Iran's top general Qassem Soleimani in a declaration they are ready for war.
It is the first time in history that the red flag has been hoisted on top of the Jamkaran mosque in the Iranian city and comes after warnings of harsh retaliation against the US, reported Metro.
Iranian state television aired the image from a mosque in the Shiite holy city of Qom, showing the flag flying above the minarets.
Red flags in Shiite tradition symbolise both blood spilled unjustly and serve as a call to avenge a person who is slain.
What is the meaning of red religious flag?
Iran has hoisted a red religious flag warning of a severe battle to come.
For the first time, the flag was unfurled on the great mosque of Jamkaran, a Shia pilgrimage site, in the Iranian holy city of Qom.
It calls for avenging Imam Hussein, the grandson of the Prophet Mohammed, who was slain during a bloody battle in Karbala. Hussein is a central figure in Shia Islam.
The flag's slogan – "O' Avengers of Hussein" – was popularized in the uprising that followed Hussein's death.
Its resurfacing in Iran serves as an ominous signal of Iran's expected response to the US assassination of its most powerful military commander, Qassem Soleimani. Tehran has vowed "forceful revenge" for his killing.
'Who is going to avenge my father's blood?
Last night Khamanei and Rouhani consoled Soleimani's family.
'Who is going to avenge my father's blood?' One of the commander's daughters asked.
In response, Rouhani promised her that 'everyone will take revenge' and assured her as she wept, 'we will, we will avenge his blood, you don't worry.'
'The Americans did not realize what a grave mistake they have made. They will suffer the consequences of such criminal measure not only today, but also throughout the years to come,' Rouhani said.
'This crime committed by the US will go down in history as one of their unforgettable crimes against the Iranian nation.'
Soleimani, 62, was killed in the early hours of Friday, local time, outside Baghdad's International Airport in an airstrike ordered by President Donald Trump.
Hours after the attack, Trump said that he ordered the killing of Soleimani to prevent war, adding that the commander was plotting 'imminent and sinister' attacks against Americans.