A series of suicide and car bombings in Iraq killed at least 61 people on Tuesday, the eve of the 10th anniversary of the US-led invasion, dpa reports.
Most of the casualties were in Shiite-dominated neighbourhoods of Baghdad, where 45 people died, police said.
More than 100 people were injured.
Security forces arrested 26 people in the capital who were carrying explosives and rockets to be used in further attacks.
A vegetable market in al-Sadr, in northern Baghdad, and a bakery in Zaafaraniya in the south, were among the targeted areas.
In the province of Babil, some 70 kilometres south of Baghdad, two suicide car bombs killed six people and injured 14.
In the northern city of Mosul, gunmen targeted a tribal leader, a policeman and an army officer.
Shortly after, a suicide bomber detonated his explosives-laden belt inside a restaurant, killing seven people.
US State Department spokeswoman Victoria Nuland said: "Senseless violence such as this tears at the fabric of Iraqi unity."
"We will continue our efforts to work with the government of Iraq to combat al-Qaeda and other threats to peace and security and unity in the country," she said.
"That is the basis of our strategic partnership with Iraq and all the work we do together on security, on economic development, on stability across the country. Still difficult, but extremely important."
UN Secretary General Ban Ki-moon condemned "in the strongest terms" the attacks.
Ban said in a statement he sent his "deepest condolences" to families of the victims as he met with the UN special representative for Iraq, Martin Kobler, to discuss the situation in that country.
The government has, meanwhile, postponed provincial council elections in two provinces, Anbar and Nineveh, for a maximum period of six months because of the security situation.
A widening rift between the Shiite-led government and Iraq's once dominant Sunni minority has raised fears of a return to the sectarian violence that drove the country to the brink of civil war in 2006-07.
Violence has been on the increase since the withdrawal of US troops in December 2011, less than a decade after the 2003 invasion that toppled Saddam Hussein.