Pilgrims in Karbala hold up Palestinian flags amid the war in Gaza as they mark annual mourning for martyrdom of Imam Hussein.

More than 21 million Shia Muslims took part in the Arbaeen pilgrimage in Iraq this year, marking the 40th day of mourning for the martyrdom of Imam Hussein, the grandson of the Prophet Mohammed and a founding figure in Shia Islam.

The event peaked on Sunday, with attendees displaying their support for Gaza.

Arbaeen, which means 40 in Arabic, is one of the world’s biggest religious gatherings and a major event for Shia Muslims, who are the majority in Iraq and Iran.

Karbala, where Hussein and his brother Abbas are buried in two enormous mausoleums facing each other, is the centre of the Shia world during this time.

Pilgrims freely express their suffering, weeping and wailing in memory of Hussein, who was killed in 680 during a battle in Karbala with the Umayyad caliph Yazid.

This year, the events have included prominent displays of Palestinian flags by pilgrims amid the war in Gaza.

“The total number of Arbaeen pilgrims… reached 21,480,525,” the institution that manages the Abbas mausoleum and is responsible for the count said.

Among them were about 3.5 million Iranian pilgrims, according to official figures reported in Tehran.

Mohammed al-Tamimi, a 32-year-old pilgrim, told the AFP news agency that the Palestinian flags waving among the pilgrims were “in support of our brothers in Palestine and in response to the Zionists, saying that Muslims stand as one against the Zionist actions and against the crimes taking place in Gaza”.

Israel has killed more than 40,000 Palestinians in Gaza since October. An estimated 1,139 people were killed during a Hamas-led attack on southern Israel on October 7.

The Arbaeen celebrations, which always take place amid tight security, drew about 22 million pilgrims last year, according to official figures. Iran provided the most foreign visitors, with 4 million.