The health ministry strongly suspects the deaths, which occurred in the Abu Ghraib area near Baghdad, were the result of a cholera outbreak first reported a week earlier.
"Last week, we announced that there 12 cases of cholera in Abu Ghraib and Najaf," health ministry spokesman Rifaq al-Araji said, referring to the holy Shiite city south of the capital.
"Since then, other cases have appeared in Abu Ghraib, and the reason is water that is not suitable for drinking," he said.
"We now have four dead in Abu Ghraib in suspected cholera cases," he said, adding that official laboratory results would be known soon.
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He said the minister had visited the hospital in Abu Ghraib, and that more medical staff were dispatched to the area and a crisis cell set up to deal with the outbreak.
The latest confirmed cholera outbreak in Iraq killed four people in 2012 in the northern autonomous region of Kurdistan.
After a short incubation period of two to five days, cholera causes severe diarrhoea, draining the body of its water.