Twelve car bombs, mainly targeting Shiite-majority areas in and around Baghdad, killed at least 47 people, while at least three died in a blast targetting Sunni worshippers, officials said.
The bombings were the latest in a string of sectarian attacks in central Iraq that have raised the spectre of a return to the intense Sunni-Shiite violence that peaked in 2006-2007 and killed tens of thousands of people.
The United States condemned the attacks as "detestable and disgraceful."
"The terrorists who committed those attacks are a shared enemy of the United States, Iraq and the international community," State Department spokeswoman Jen Psaki said.
The car bombs struck nine different areas, six of them Shiite-majority, one confessionally mixed and two Sunni-majority, also wounding more than 140 people.
The deadliest attacks hit Kadhimiyah, a mainly Shiite area of north Baghdad, where two car bombs killed at least nine people and wounded another 19.
In Baghdad Jadida, a bomb exploded in a car park, burning vehicles, destroying a fence and shattering the windows of nearby shops and a women's clinic, an AFP journalist reported.
Security forces deployed to the area, closing off streets and using sniffer dogs to search for more bombs.
Later on Monday, a bomb exploded as worshippers left Al-Mustafa Mosque in the Dura area of south Baghdad, killing at least three people and wounding at least 12.
Central Iraq has seen a series of sectarian attacks on mosques and funerals in recent days.
On Sunday, a suicide bomber attacked mourners at a Shiite mosque south of Baghdad, collapsing the roof and killing 47 people.
On Friday, bombs exploded near two Sunni mosques in Baghdad as worshippers left after prayers, killing six people.
Another bombing targeted Sunni mourners in Baghdad on September 23, killing 15 people, while an attack on a Sunni funeral killed 12 the day before.
Bombings targeting Shiite mourners killed 73 people in Baghdad on September 21, and two blasts at a Sunni mosque north of the capital killed 18 a day before that.
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The UN refugee agency has said it is "increasingly concerned about the situation in Iraq, where recent waves of sectarian violence threaten to spark new internal displacement of Iraqis fleeing bombings and other attacks."
It said that about 5,000 Iraqis had already been displaced in 2013, joining more than 1.13 million who fled or were forced out of their homes in past years.
Attacks also hit Diyala and Nineveh provinces on Monday, killing two people and wounding one.
Monday's violence came a day after a rare attack in Arbil -- the usually quiet capital of Iraq's autonomous Kurdish region -- which killed seven security forces members and wounded more than 60 people.
The three-province northern region has largely been spared the attacks plaguing other areas of the country.
Violence in Iraq has reached a level not seen since 2008, when the country was just emerging from its brutal sectarian conflict.
Diplomats and analysts say the Shiite-led government's failure to address the grievances of the Sunni Arab minority -- which complains of political exclusion and abuses by security forces -- has driven the spike in violence.
Violence worsened sharply after security forces stormed a Sunni Arab anti-government protest camp in northern Iraq on April 23, sparking clashes in which dozens of people were killed.
The authorities have made some concessions aimed at placating anti-government protesters and Sunnis in general, such as freeing prisoners and raising the salaries of Sunni anti-Qaeda fighters, but many underlying issues have yet to be addressed.
The civil war in neighbouring Syria has also fuelled sectarian tensions in Iraq.
The latest bloodshed brings the September death toll to more than 870, according to AFP figures based on security and medical sources. Upwards of 4,700 people have been killed so far this year.
In addition to major security problems, the government has failed to provide adequate basic services such as electricity and clean water, and corruption is widespread.
Political squabbling has paralysed the government, while parliament has passed almost no major legislation in years.