KARBALA, Iraq — Millions of Shiite Muslims packed the streets of the Iraqi city of Karbala Saturday on their annual pilgrim to mark the death of Prophet Muhammad’s grandson, Hussein, who became a symbol of resistance during the tumultuous first century of Islam’s history.

Tahseen Al-Khafaji, head of the Iraqi security media cell, said that more than 3 million pilgrims had entered the country as of Friday, amid tight security measures.

This year Arbaeen - Arabic for the number 40 and traditionally observes the end of a mourning period - was shrouded with sadness over the war in Gaza, now in its 11th month, and worries it may expand into a regional conflict with tensions spiking between Israel and Iran after a blast killed the leader of the Palestinian militant group Hamas, Ismail Haniyeh, in Tehran last month.

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Hussein’s death exacerbated the schism between Islam’s two main sects, Sunni and Shiite. However, for many Muslims, that division has now taken a back seat to shared anger and grief over the suffering of Palestinians in Gaza where more than 40,000 have so far been killed. The Israel-Hamas war broke out following the group’s surprise attack on southern Israel, killing nearly 1200 people and taking 250 others hostage.

Pilgrims usually flock from all around the world to honor Arbaeen on the 20th day of Safar, the second month of the Islamic lunar calendar every year, which culminates at the spot where Hussein and his half-brother Imam Abbas were killed during the Battle of Karbala. Many view it as a reminder of the unity of the Shiite community through centuries of turmoil.

“May God never take away this solidarity among us,” said Amad Zarepoor, who arrived from Iran.

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PHOTOS: Millions of Shiite Muslim pilgrims head to Iraq's Karbala to mark the death of Imam Hussein

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On Saturday, the rhythmic sound of pilgrims pounding their chests and heads as they circled the Imam Hussein Shrine filled the air.

One of the busiest points is the Iraq-Iran border crossing of Mandali in Iraq’s northern province of Diyala. Sinan al Shemmeri, a spokesperson for the Popular Mobilization Forces, a coalition of mostly Shiite Iran-allied militias, said the crossing “is not only for Iranian brothers but for various other nationalities, such as Azerbaijan and Pakistan.”

Volunteers could be seen lining the nearly 113-kilometer (70-mile) road from Iraq’s capital, Baghdad, to Karbala, offering food to weary pilgrims.

“Everything we offer is to commemorate and serve our Master (Hussein),” said Hussein Ali, a volunteer in Baghdad.

Iranian pilgrim Ali Bagheri expressed his happiness with Iraqi hospitality. “I’m again a guest of Iraqis,” he said, “I’m very happy I can walk down this path with Iraqis and we can make a pilgrimage.”

Despite the celebration, this year’s Arbaeen was also marred by a bus accident in central Iran on Wednesday that left 28 passengers dead and 23 others injured, 14 critically.