The death toll from a suicide bombing in a Baghdad shopping district rose above 175, fuelling calls for security forces to crack down on Islamic State sleeper cells blamed for one of the worst-ever single bombings in Iraq.
Numbers rose as bodies were recovered from the rubble in the Karrada area of Baghdad, where a refrigerator truck packed with explosives blew up on Saturday night when people were out celebrating the holy month of Ramadan.
By Monday evening, the toll in Karrada stood at 175 killed and 200 wounded, according to police and medical sources, while 37 people are still missing.
IS claimed the bombing, its deadliest in Iraq, saying it was a suicide attack.
Another explosion struck the same night, when a roadside bomb blew up in popular market of al-Shaab, a Shi'ite district in north Baghdad, killing two people.
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The attacks showed IS can still strike in the heart of the Iraqi capital despite recent military losses, undermining Prime Minister Haider al-Abadi's declaration of victory last month when Iraqi forces dislodged the hardline Sunni insurgents from the nearby city of Fallujah.
In a sign of public outrage at the failure of the security services, Abadi received an angry reception on Sunday when he toured Karrada, the district where he grew up, with residents throwing stones, empty buckets and even slippers at his convoy in gestures of contempt.
He ordered new measures to protect Baghdad, starting with the withdrawal of fake bomb detectors that police have continued to use despite a scandal that broke out in 2011 about their sale to Iraq under his predecessor, Nuri al-Maliki.
The hand-held devices were initially developed to find lost golf balls, and the British businessman who sold them to Iraq for $US40 million ($A53.71 million) was jailed in Britain in 2013.
Later on Monday, the justice ministry announced in a statement that five people convicted of terrorism and sentenced to death were executed on Monday morning, bringing the total number of those executed on the same charges to 37 in the past two months.
Iraqi intelligence services also announced on Monday the arrest of 40 "terrorists" suspected of forming a group to carry out attacks in Baghdad and the eastern Diyala province.
As Iraq started observing three days of national mourning, rescuers continued digging through the rubble of a shopping mall believed to be the main target of the bombing, searching for bodies or possible survivors.
Three bodies were pulled out in the morning from the basement of the three-story Al-Laith mall, which was reduced to a skeleton of charred steel and concrete by the blast.
