At least nine Iranian pilgrims died and dozens were injured when a bus carrying them collided with a truck in the southern Iraqi city of Nassiriya on Monday.

The bus was crammed with pilgrims en route to the city of Karbala, where Shiite Muslims commemorate Arbaeen religious ceremony.

Arbaeen (literally meaning fortieth) is a Shiite religious observance that occurs forty days after the Day of Ashura, when according to religious legend Husayn (Hussain) ibn Ali, the grandson of Prophet Muhammad was killed on the 10th day of the month of Muharram in 680 AD.

A medical source told Reuters that 31 people, including women and children, were injured and five of them were in a critical condition.

The Islamic Republic regime views the event as a show of influence in the region, encouraging high participation via numerous perks, including providing free medical services and rest stops along the way, free internet on the road and inside Iraq, offering interest-free loans and granting 200,000 Iraqi dinars ($153) to pilgrim as well as special passports with less bureaucratic requirements. The ration of cheap foreign currency – which used to be dollars or euros until this year – will be paid from Iran's frozen funds in Iraq, about to be released as part of a prisoner swap deal with the United States.

Despite the incentives, the number of Iranians willing to undertake the Arbaeen Shiite pilgrimage is in decline.