The US State Department confirmed that at least 80 people, mostly Iranian Shi'ite pilgrims were killed and 50 others injured on 24 November when a truck bomb exploded at a gas station in Iraq.
The Islamic State has claimed responsibility for the attack in a statement posted online.
"The flames of battles in Mosul will reach them in Baghdad, Karbala and Najaf," the ISIS statement reads, according to CNN.
The parked truck exploded near several buses carrying Shi'ite pilgrims, who were in Iraq to commemorate Imam Hussein's death.
According to ABC News, most of those who died in the blast were Iranian Shia pilgrims participating in an Arba'een pilgrimage -- an annual religious event in the holy city of Karbala.
Hussein was the grandson of the Prophet Mohammed and was killed during a battle near Karbala for control of the Muslim nation.
Hussein's 7th-century death led to a split between Sunni and Shi'ite Muslims that still divides the sects today. Despite ongoing dangers, Shi'ite pilgrims still make the journey to Karbala.
The attack by the Islamic State was the latest aimed at the followers of Shia Islam. In July, more than 300 people were killed reportedly in an attack on a commercial district and in May Car bombings reportedly took around 100 lives.
--with ANI inputs