A car bomb claimed by Islamic State in a Shiite Muslim district of Baghdad killed 50 people on Wednesday, Iraqi police and hospital sources said.
At least 60 others were wounded in the blast and many remained in critical condition, the sources added.
The SUV packed with explosives went off in a bustling market at rush hour in Sadr City.
Amaq news agency, which supports Islamic State, said a suicide bomber had targeted Shiite militia fighters.
The ultra-hardline Sunni terror group, which considers Shiites apostates, claimed a twin suicide bombing in Sadr City in February that killed 70 people.
The fight against Islamic State has exacerbated a long-running sectarian conflict in Iraq, mostly between the Shiite majority and the Sunni minority.
Sectarian violence also threatens to undermine efforts to dislodge the militant group from vast areas of the north and west of Iraq that they seized in 2014.