At least one person was killed and four more were injured in Karbala, one of the holiest sites in Shiite Islam, in Iraq. Currently, the site is witnessing one of the largest religious gatherings in the world for the festival of Arbaeen on Saturday, which will mark the end of the 40-day mourning period for the death of Imam Hussein.

"There were one person killed and four wounded when mortar rounds hit an area on the western side of the city," shortly after midnight, a police official said, according to Agence France-Presse (AFP), adding: "They crashed into an area called Souk al-Basra, around seven kilometers (four miles) from the city centre."

Hussein is one of the most important figures for Shia Muslims, who form a majority in Iraq as well as in neighboring Iran. Over 17 million pilgrims have reached Karbala for this year’s Arbaeen, making it the largest gathering in the world for 2014, AFP reported. The gathering also comes at a time when the Sunni Islamic State group has stepped up its offensive against the country's Shias, who the group calls heretics.

Earlier this week, three people were killed and four were injured in an attack when a bomb exploded in Baghdad, where several Shiite pilgrims were being served food and beverages, AFP reported.