Attacks, including bombs that exploded in a market near a church in Baghdad, killed at least 40 people across Iraq on Wednesday, officials said.
The bloodletting comes as Iraq suffers its worst violence since 2008, when it was just emerging from a brutal period of sectarian killings, raising fears that the country is slipping back into all-out conflict.
"Two roadside bombs exploded in a popular market in Dura, killing 35 people and wounding 56," interior ministry spokesman Saad Maan told AFP, referring to a south Baghdad area.
Militants frequently attack places where crowds of people gather, including markets, cafes and mosques, in an effort to cause maximum casualties.
Security officials had initially said that a car bomb targeted the St. John church in Baghdad in addition to the market blasts, but Maan, along with a priest from the area and the Chaldean patriarch, all later denied this.
"The attack was against a... market and not a church," Maan said, while adding that "the targeted area is a mix of Muslims and Christians."
Archdeacon Temathius Esha, an Assyrian priest in Dura, and Chaldean Patriarch Louis Sako both also insisted that the church was not the target.
Other attacks on Wednesday left five more people dead.
A bombing in south Baghdad killed at least one person and wounded at least three, while gunmen killed three police near Tikrit, north of Baghdad, and bombs on the road between Kirkuk and Tuz Khurmatu, also north of the capital, killed one person and wounded seven.
Analysts say widespread discontent among Iraq's minority Sunni Arab community is a major factor fuelling the surge in unrest this year.
But although the government has made some concessions aimed at placating Sunni Arabs, including freeing prisoners and raising the salaries of Sahwa anti-Qaeda fighters, underlying issues remain unaddressed.
The bloody 33-month civil war in Syria, which has bolstered extremist groups, has also played a role.
Defence ministry spokesman Mohammed al-Askari told AFP that aerial photographs and other information pointed to "the arrival of weapons and advanced equipment from Syria to the desert of western Anbar and the border of Nineveh province," referring to Sunni-majority areas bordering Syria.
This has encouraged Al-Qaeda-linked militants to "revive some of their camps that were eliminated by security forces in 2008 and 2009," Askari said, adding that aerial photos showed 11 militant camps near the border with Syria.
Iraqi security forces have launched an operation against militants dubbed "Avenge the Leader Mohammed" after a divisional commander who was killed during a raid targeting militants.
The defence ministry said in an online statement issued Wednesday that security forces had killed 11 militants in a three-day period, as well as capturing weapons and equipment.
But Iraqi forces responded to the rampant violence with military operations earlier this year as well, and the deadly attacks have continued unabated.
It took just the first eight days of this month for the death toll to exceed 144 -- the number of people killed in all of December last year.
And more than 6,700 people have been killed in Iraq since the beginning of 2013, according to AFP figures based on security and medical sources.