Attacks mainly targeting Shiite-majority areas of Iraq killed at least 57 people, and security forces killed 10 militants, officials said, as the interior ministry warned of civil war.
UN Secretary General Ban Ki-moon also warned that Iraq was "on the brink", with the country suffering its worst wave of violence since 2008, when it was emerging from a bloody sectarian conflict.
On Monday, 11 car bombs hit nine different areas of Baghdad, seven of them Shiite-majority, while another exploded in Mahmudiyah south of the capital.
Two more car bombs exploded in Kut, while two hit Samawa and another detonated in Basra, all south of Baghdad.
Bombings elsewhere in Iraq killed six police, among them a lieutenant colonel and a captain, in addition to a soldier and two civilians.
More than 800 people have now been killed this month, and over 3,000 since the beginning of the year, according to AFP figures based on security and medical sources.
The violence has included sophisticated, highly coordinated attacks, such as assaults on two prisons that saw more than 500 inmates, including senior Al-Qaeda members, escape.
The interior ministry warned of the consequences of the bloodshed.
Iraq is faced with "open war waged by the forces of bloody sectarianism aiming to plunge the country into chaos and reproduce civil war", the ministry said in a statement.
"Iraq is at another crossroads," UN chief Ban was quotes as saying in a statement released by spokesman Eduardo del Buey.
"Its political leaders have a clear responsibility to bring the country back from the brink, and to leave no space to those who seek to exploit the political stalemate through violence and terror."
Iraq was racked by a bloody Sunni-Shiite sectarian conflict that peaked in 2006-2007, when thousands of people were killed because of their religious affiliation or forced to abandon their homes under threat of death.
Army and police forces, meanwhile, killed 10 militants west of Tikrit, police said.
They also destroyed the militants' camp, carried out controlled detonations of three car bombs and seized explosives belts, rocket-propelled grenade launchers, ammunition and explosives, they said.
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One of the Baghdad bombs exploded near where day labourers wait for work in the overwhelmingly Shiite area of Sadr City, killing five people and wounding 17.
Debris, including what appeared to be the remains of the vehicle that held the explosives, covered the street around the site of the blast, badly damaging surrounding shops, an AFP journalist reported.
Monday's violence came a day after attacks killed 14 people, among them nine Kurdish policemen who died in a suicide bombing in the northern town of Tuz Khurmatu.
Militants have carried out two highly coordinated operations in recent days, highlighting both their growing reach and the rapidly worsening security situation.
Last week, some 150 militants attacked the northern town of Sulaiman Bek, drawing security forces away from the main highway.
About 40 militants then broke off, set up a checkpoint on the road, and killed 14 Shiite truck drivers.
The highway killings were reminiscent of the darkest days of the Sunni-Shiite sectarian bloodshed.
Lingering tensions between Sunnis and Shiites have been inflamed by persistent violence in Iraq and the civil war in neighbouring Syria, and there are growing fears that the country is slipping back towards all-out sectarian conflict.
And on the night of July 21, militants launched brazen assaults on Abu Ghraib and Taji prisons, sparking clashes that lasted for some 10 hours.
At least 500 prisoners including Al-Qaeda inmates escaped and at least 20 security forces members and 21 inmates were killed.
Iraq has faced years of attacks by militants, but analysts say widespread discontent among the Sunni Arab minority that the government has failed to address has fuelled this year's surge.
Sunnis accuse the Shiite-led government of marginalising and targeting their community, including through unwarranted arrests and terrorism charges.
Protests that erupted in Sunni areas at the end of 2012 are still ongoing.
In addition to major security problems, the Baghdad government is also failing to provide adequate basic services such as electricity and clean water, and corruption is widespread.
Political squabbling has paralysed the government, which has passed almost no major legislation in years.