Iraqi men carry a victim of a suicide attack in the Dura area of south Baghdad on December 19.

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NEW: Three bombings kill at least 31 Shiite pilgrims south of Baghdad

Another 75 people were wounded

Similar attacks have taken place in recent years

Separately, gunmen killed a family of four in northern Baghdad

CNN  — 

A string of suicide bombings killed at least 31 Shiite pilgrims Thursday in Iraq, police said.

The first attack killed 18 people in addition to the bomber, and left 35 people wounded, police said.

The second left seven dead in addition to the bomber and 22 wounded.

The third killed six people, plus the bomber, and left 18 wounded.

The attacks took place south of Baghdad as thousands of pilgrims walked toward Karbala for al-Arbaeen, a 40-day period marking the death of Imam Hussein.

Similar attacks have taken place every year in recent years.

Separately, all four members of a family – a father, mother and their two children – were shot dead in their sleep by gunmen in northern Baghdad, police said. The father used to be a member of a local awakening council.

The councils are made up mostly of Sunni fighters who turned against al Qaeda in late 2006. The movement is backed by the United States and is a target for jihadists.