A torrent of bombings and shootings have ripped across eight Iraqi cities, targeting police and Shi'ite pilgrims and killing 46 people.
The deadly wave undermined the government's hopes for stability ahead of next week's meeting of the Arab world's top leaders.
The Iraqi wing of al-Qaeda said it was behind at least one of the attacks near Baghdad's heavily guarded Green Zone.
A statement on a militant website said the group targeted the office that will oversee security for the upcoming Arab League summit - the first time the meeting is set to be held in Baghdad for more than a generation.
"Death is approaching you when you least expect it," said the Islamic state of Iraq, a local front group for al-Qaeda.
Authorities have feared al-Qaeda or its Sunni sympathisers would try to thwart this year's Arab League summit. Plans for Baghdad to host the meeting last year were postponed, in part because of concerns about Iraq's security.
In all, eight cities were hit on Tuesday in what appeared to be coordinated attacks against police and government officials. More than 200 people were wounded in a gloomy reminder of the violence that has sown chaos across Iraq since the US invasion exactly nine years ago.
One of the deadliest strikes came in the Shi'ite holy city of Karbala, where officials said two car bombs exploded in a crowded shopping and restaurant area. Thirteen people were killed and another 50 were wounded in that assault, said local provincial council member Hussein Shadhan al-Aboudi.
Five Iranian pilgrims were among the dead. Located 80 kilometres south of Baghdad, Karbala is a destination for thousands of Shi'ite pilgrims from around the world who visit the golden shrines of two revered imams each day.
"The intention of these attacks is to destabilise the security situation in Karbala and other Iraqi cities and to shake the people's confidence on the government," al-Aboudi said. "It seems that the terrorists want to abort the upcoming Arab Summit in Baghdad. The message is directed to the Arab leaders that Iraq is not safe enough to be visited."
The wave of violence began after dawn on Tuesday.
Militants blew up the house of a police official in the western city of Fallujah, planted bombs near the fortified Green Zone and shot up a security checkpoint in Baghdad, set off an explosion at a police station in the northern city of Kirkuk and attacked restaurants and shopping areas in two southern towns.
Police and health officials in each city who confirmed the casualties spoke on condition of anonymity because they were not authorised to speak to the media.
Saman Majid, a cameraman for the Kirkuk police department said he had just arrived at work when the bomb outside the station exploded. He said he was wounded by small shrapnel that hit his head and ran to the Kirkuk General Hospital for treatment instead of waiting for an ambulance.
"I quickly got out of my car to see burned bodies trapped inside the cars," he said. "Dozens of cars were on fire. It was a scene from hell, where there is only a huge fire and dead people and nothing else."
Thirteen people, most of them policemen, were killed in Kirkuk, said Brigadier General Sarhad Qadir. An additional 59 were wounded. Kirkuk is 290 kilometres north of Baghdad.
Officials have been bracing for attacks in the run-up to the Arab League summit during which the Shi'ite-led government hopes to showcase Iraq's improved security and stability since the sectarian fighting a few years ago that almost pulled the country into civil war.
Insurgents are seeking to belie Baghdad's better image, and officials expect more attacks as hundreds of dignitaries and journalists converge on the capital next week.
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