Iraqi Defence Minister Khaled al-Obeidi said Thursday that the number of pilgrims in the city of Karbala for the annual Arbaeen commemoration had reached a record 17.5 million this year.
Arbaeen, which marks the end of the 40-day period of mourning after the anniversary of Imam Hussein's death, is considered one of the largest religious gatherings in the world.
"The number of Arab and foreign pilgrims has reached 4.5 million, of 60 different nationalities, the biggest contingent being Iranians," he told reporters.
"And until today, we had 13 million Iraqis," he said.
The Arbaeen commemoration is on Saturday December 13, but millions of Shiite faithful have been walking to Karbala from all over Iraq, and large numbers from across the Iranian border, for days.
The Iraqi authorities had reported already last week that at least one million Iranians, the largest number on record, had come to Iraq for Arbaeen this year.
The crowds are so huge it is difficult to verify the figures provided by the authorities, but the governor of Karbala said it was the largest attendance ever.
"This is the biggest. It's exceptional because the pilgrims consider this as an act of defiance in the face of the terrorist gangs of Daesh," Aqil al-Turaihi said.
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He was referring to the Islamic State jihadist group which launched an offensive in Iraq in June and conquered entire swathes of the country.
Obeidi said the number of pilgrims was so high the country's top brass had to revise its security plan and open new access routes to Karbala, a medium-sized city about 70 kilometres (45 miles) south of the capital Baghdad.
The pilgrimage comes only weeks after a major victory against the jihadists in the Jurf al-Sakhr area between Karbala and Baghdad.
The continued presence there of IS fighters would have exposed the millions of southbound pilgrims walking through an area which has seen some of the worst sectarian violence of the past decade and has been dubbed the "triangle of death".
Most of the men now defending Jurf al-Sakhr, a sprawling area of farmland and palm groves nestled along the Euphrates, are from Shiite militias who fought alongside the army and with Iranian assistance, to recapture the strategic site.
"The victories obtained here have had a great impact on the march" of the pilgrims, Communications Minister Hassan al-Rashed said Wednesday when he visited Jurf al-Sakhr.
Rashed is also a commander in the Badr organisation, which also holds the interior ministry in Iraq's new government and whose military wing is one of the largest Shiite militias in the country.
"Today all the areas surrounding Karbala are safe, thanks to the efforts they (Badr fighters) made, the blood they spilled and the sacrifices they made, in coordination with the security forces," he said.
Shiite pilgrims have been targeted in the past, but few attacks have been reported against those heading to Karbala this year.