The deadliest attack hit the Dura area of south Baghdad, where a bomber targeted pilgrims at a tent where they are served food and drinks on their way to the shrine city of Karbala, killing at least 20 people and wounding at least 40.
Among those killed in the blast was Muhanad Mohammed, a journalist who had worked for both foreign and Iraqi media, one of his sons told AFP.
He was the seventh journalist to be killed in the country in less than three months.
At Yarmuk Hospital in Baghdad, wounded people were rushed in on gurneys for treatment, and those injured included children and an old woman whose face was covered in blood.
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One distraught man in the lobby of the surgery department repeatedly struck himself in the face with both hands, overcome with grief.
In the street outside, empty wooden coffins were mounted on vehicles, while people cried and screamed over the loss of loved ones.
Hundreds of thousands of people make pilgrimages to the city of Karbala, many of them on foot, during the 40 days after the annual commemoration marking the death of the Prophet Mohammed's grandson, known to Shiites as Imam Hussein.
Sunni militants, including those linked to Al-Qaeda, frequently target members of Iraq's Shiite majority, whom they consider to be apostates.
The throngs of pilgrims on the roads make for an easy target, and they have been hit by a series of attacks in the past few days.