At least 54 people have been killed and many others injured in a series of car bomb attacks in central and southern Iraq, officials say.
Baghdad was worst hit, with nine explosions at bus stations and markets in the mainly Shia Muslim districts.
Two bombs went off earlier in the day in the southern city of Basra, and a blast in Samarra killed three people.
The attacks are part of the recent rise in violence in Iraq linked to growing political and sectarian tension.
Police said nearly 200 people were injured in Monday's violence in Iraq. Eight Iranian pilgrims are reported to be among the dead.
One of the bloodiest attacks in Baghdad happened in the northern Shia neighbourhood of Shaab, when a car bomb exploded near a crowded market place killing at least 12 people and wounding more than 20.
The bombs in Basra, a mainly Shia Muslim city, killed at least 14 outside a restaurant and the main bus station.
"We were sitting here waiting for work and as usual we gathered near a street food cart and the place was very crowded," Basra resident Mohammed Ali, who was near one of the blasts, told Reuters news agency.
"I crossed the street to the other side when all of a sudden it turned dark, dust filled the area. I was showered with metal wreckage and wounded in my legs."
A further three people were killed and 15 wounded in a car bomb attack in Samarra, a city some 113km (70 miles) north of Baghdad. The blast reportedly happened near a gathering of members of the pro-government Sunni militia, the Awakening Council.
In a separate incident, 10 policemen kidnapped on Saturday in western Anbar province have been found dead.
No group has said it carried out Monday's bomb attacks, but tension between the Shia Muslim majority, which leads the government, and minority Sunnis has been growing since last year.
Sunni demonstrators have accused the government of Prime Minister Nouri al-Maliki of discriminating against them - something the government denies.
Iraqis have not witnessed violence on the scale of the last few weeks for nearly five years, says the BBC's Aleem Maqbool in Baghdad.
The Shia-Sunni fault line, with Syria currently at its epicentre, is certainly contributing, he notes.
But Iraqis do not see their own politicians doing enough to unite people on both sides of the sectarian divide, and they do not see the international community showing the urgency they think it should in averting further chaos, our correspondent adds.
Violence has increased since more than 50 people died in clashes between security forces and Sunni Arabs in April, when an anti-government protest camp was raided in Nawija near Kirkuk.
At least 60 people died in three bombings in Sunni Muslim areas in and around Baghdad on Friday. Those bombings followed deadly attacks on Shia targets across Iraq.
On Sunday, at least 10 policemen were reported killed in north-western Iraq in attacks blamed by the authorities on Sunni militants.
Basra had been seen as relatively peaceful, but there too, violence has risen in recent months.
In March, a car bomb in the city killed 10 and wounded many others. On Saturday gunmen there shot and killed a Sunni Muslim cleric.
The increasing number of incidents has raised fears that Iraq could return to the worst of the sectarian conflict seen in 2006 and 2007.
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