At least 119 people were killed and 200 injured in two bombings that hit Baghdad overnight.
The majority of those who died were killed in a blast targeting a busy shopping area as they celebrated Ramadan, police and medical sources said.
A refrigerator truck packed with explosives blew up in the district of Karrada, killing 117 people and injuring over 200.
So-called Islamic State claimed responsibility for the attack, in a statement circulated online by supporters of the ultra-hard line Sunni group. It said the blast was a suicide bombing.
Karrada was busy at the time as Iraqis eat out late during the Muslim fasting month of Ramadan, which ends next week.
A video posted on social media showed a large blaze in the main street of Karrada after the blast.
A roadside explosive device also blew up around midnight in a market in al-Shaab, a popular Shia district in the north of the capital, leaving at least two killed, police and medical sources said.
The attack on the shopping area of Karrada is the deadliest since US-backed Iraqi forces last month scored a major victory when it dislodged IS from their stronghold of Fallujah, an hour's drive west of the capital. It is also the deadliest so far this year.
Prime Minister Haider al-Abadi had ordered the offensive after a series of bombings in Baghdad, saying Fallujah served as a launch pad for such attacks on the capital. However, bombings have continued.
A convoy carrying Mr Abadi who had come to tour the site of the bombings was pelted with stones and bottles by residents, angry at what they felt were false promises of better security.
The White House said the attack only strengthened the United States' resolve to confront IS. "We remain united with the Iraqi people and government in our combined efforts to destroy ISIL," said the White House statement, referring to Islamic State.
Mr Abadi declared three days of mourning for the victims, according to state-run media that also cited him saying he understood the angry reaction of residents.
