(CNN) At least 31 people were killed and more than 100 wounded in a stampede in the Iraqi city of Karbala, as Shia Muslim worshipers commemorated Ashura on Tuesday, according to Iraq's health ministry.

Thousands had jammed the streets to attend festivals marking the most important Shia holy day of the year.

Police officials are investigating the circumstances that led to the stampede, security officials told CNN.

Ambulances rushed to the scene to evacuate the wounded.

Ashura is the anniversary of the death of Imam Hussein, grandson of the Prophet Mohammed.

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