A suspected female suicide bomber blew herself up on Monday among Shi'ite visitors on the outskirts of the Iraqi capital, killing at least 41 people, the office of the Baghdad security spokesman said.
The attack took place as thousands of Shi'ite Muslims flooded the streets at the start of an arduous trek to the southern city of Kerbala, 80 km (50 miles) southwest of Baghdad, for the religious rite of Arbain.
A Interior Ministry source and a police official said 41 people died and 106 were wounded in what they said was an attack on a tent where pilgrims are given food and drink.
The office of Baghdad security spokesman Major General Qassim al-Moussawi said the attack occurred in a crowd and that 19 people were killed, with 80 wounded.
Arbain marks 40 days of mourning for Hussein, the Prophet Mohammad's grandson (PBUH), who died in a seventh century battle at Kerbala.
Many walk from hundreds of kilometres (miles) away.