Four Iraqis were killed and more than 20 wounded on Saturday in a bus explosion in Baghdad's Kadhumiyah Shiite neighborhood, police said.

The blast took place outside a security barrier set up to keep vehicles away from the Shiite Imam Kadhum shrine in northern Baghdad, they said.

Shiite Muslims in Iraq began to celebrate their most important holiday of Ashura in Baghdad, which falls on Feb. 19 this year according to Muslim's lunar calendar.

The bus explosion came one day after five attacks targeting Iraq's Shiite muslims and security forces in Baghdad left at least 30 dead.

Last year's commemoration of Ashura was marred by bombings in Baghdad and Karbala that killed some 170 people.