A blood-red flag symbolizing vengeance unfurled Saturday above the dome of Jamarkaran Mosque in Qom, Iran, a day after the United States killed Iranian Gen. Qassem Soleimani and Iraqi militia leader Abu Mahdi al Muhandis.

The flag, inscribed with the words "Those who want to avenge the blood of Hussein," was hoisted above the mosque's shrine for what local reports claimed was the first time in history, according to the Daily Mail.

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The grandson of Muhammad, Hussein was decapitated in A.D. 680 during the Second Islamic Civil War, when Muslims were fighting over who was the proper successor to their prophet. The act was met with bloody retaliation from Muslims who considered Hussein's death unjust and sought to avenge him.

Very very unusual to see a red flag flying over holy mosque of Jamkaran in Qom, Iran‘s holiest city. It’s is almost always blue. The red flag symbolises revenge. pic.twitter.com/0VeWvUY37L — Ali Arouzi (@aliarouzi) January 4, 2020

The symbolic act took place the same day that many took to the streets of Baghdad to shout "Death to America!" during the funeral processions of Soleimani and al Muhandis. Iran's President Hassan Rouhani comforted Soleimani's daughters Saturday, promising that "everyone will take revenge" on their father's blood. An Iranian general claimed that the country is ready to strike at least 35 American targets, including shipping channels in the Strait of Hormuz.

The daughter of Iran's top general Qassem Soleimani has asked Iranian President Hassan Rouhani who will avenge his death.



Read more on the reaction to the assassination here: https://t.co/J2gCUvLKRA pic.twitter.com/BqN49Rd0FB — Sky News (@SkyNews) January 4, 2020

Jamarkaran Mosque is one of the holiest sites in Shiite Islam and one of the mosques associated with the Mahdi, also known as the 12th Imam. Some Muslims believe the Mahdi is alive but hidden and will emerge to rule the world shortly before the Day of Judgment. Referencing the Mahdi, the speaker called, "O Allah, hasten your custodian reappearance," as the flag was raised.