Baghdad (CNN) -- At least four people were killed and 17 were wounded in a suicide bombing north of Baghdad on Monday, according to Iraq's Interior Ministry.
The suicide bomber struck a group of Shiites in the town of Balad Ruz, just east of Baquba, said Maj. Ghaleb al-Atiya, police spokesman in Diyala province.
In addition, nine other Shiite pilgrims were wounded in two separate attacks in Baghdad, an Interior Ministry official said. Five pilgrims were wounded when a mortar struck their procession in southeastern Baghdad, while four others were hurt in a roadside bombing, according to the official.
The Shiite pilgrims are preparing to observe Ashura later this week. On that day, Shiites commemorate the martyrdom of the 7th century Imam Hussain, grandson of the prophet Mohammed and one of the most revered figures in the sect.
The period leading up to such pilgrimages is historically a violent one, as the pilgrims are a target for suicide bombers and other attacks.
On Sunday, at least three Shiite pilgrims were killed and a dozen more were wounded in a similar suicide attack, also in Diyala province. Since the beginning of December, pilgrims -- many of them Iranians -- have been targeted in other suicide attacks.