At least four people were killed and 28 wounded when a car bomb exploded in a market in Sadr City in Baghdad.
Police said they feared the toll would rise from the bombing during the rush hour in the Shia militia stronghold.
Two weeks ago, bombings at two pet markets, which US and Iraqi forces said were the work of al-Qaeda, killed 99 people.
Attacks have fallen by 60 per cent across the country since June, the US military says.
