|Baghdad, Tikrit, Taji and Hilla were among the more than 15 cities targeted by Thursday's attacks [Reuters]
A series of bomb blasts and shootings in Baghdad and other areas of Iraq have killed at least 55 people and injured hundreds more, sources tell Al Jazeera.
Iraq's parliament speaker blamed al-Qaeda for Thursday's attacks, saying the attacks were an attempt to derail an Arab League summit planned for the end of March.
"The terrorist al-Qaeda organisation is trying to send messages to its supporters that it is still operating on Iraqi soil, and that it has the capability to strike in the capital and the cities and both big and small regions," a statement on the interior ministry's website said.
Al Jazeera's Jane Arraf, reporting from the Iraqi capital, said the attacks included car bombs, roadside bombs seemingly targeting police, and armed men opening fire on police patrols.
"The blasts seemed to happen at almost the same time, in what are being seen as co-ordinated attacks," our correspondent said.
"They happened in other cities as well as Baghdad," she said. "In Tikrit, Taji, and Hilla, and the common denominator seems to be that they're all targeting Shia areas, and security installations."
Two car bombs exploded in the mostly Shia Karada district in central Baghdad, killing two people and injuring at least 17 people, according to a police source.
A parked car bomb in the Kadimiyah district of northeast Baghdad, seemingly targeting a chain of restaurants where people had gathered to eat breakfast, killed six people and injured another 15.
In the Dora district, in the southwest of the city, two roadside bombs killed two people and injured 10 others.
A gathering of police patrols at the Sarafiyah bridge in the north of Baghdad was targeted by unknown armed men, who killed six policemen, and injured three more.
Reports claimed an explosion, possibly another car bomb, in the Mansour district in west Baghdad killed two people and injured five others.
Beyond the Iraqi capital, a parked car bomb in the Dujail area in south Salah al Din province killed one civilian and injured seven others.
In Taji, north of Baghdad, a roadside bomb near a school and a Shia mosque injured five people, including two boys and a girl.
A car bomb explosion in Beji, an area north of Tikrit, apparently targeting a local court, killed three people and injured 12 others.
Another car bomb planted in the south of Tikrit detonated in the Balad area near a police station, leaving four people dead and 26 others injured.
In the Touz area, east of Tikrit, a parked car bomb blew up next to the National Kurdistan Union, where two civilians were killed and eight more injured.
In the Salman Baik area, also east of Tikrit, an unknown armed group wearing police uniforms stormed into a local council building, killing two policemen and injuring three people, including the head of the local council and two policemen.
In Hilla city, south of Baghdad, two car bombs killed one person and injured five, and the other bomb, which apparently targeted a school, killed one person and injured 50 schoolchildren.
Unknown armed gunmen opened fire on a police checkpoint northeast of the Imam Waiss area in Baquba city, killing two policemen and injuring one.
Also in Baquba city, explosions targeting an Iraqi army patrol, a police station and a police intelligence building left nine people dead and eight others injured.
Two children were killed and one other wounded in an explosion at a football pitch in Mandili, east of Baquba.
Armed gunmen stormed a house belonging to a member of the National Council for the Awakening of Iraq in the Hashimiat area, killing two members of his family, and injuring one.
In Kirkuk province, two car bombs targeting a police patrol left 16 policemen injured.
Tensions have been high in Iraq as it struggles with a political crisis in the aftermath of the withdrawal of US troops from the country at the end of last year, with the country suffering several deadly bombings in recent weeks.
On Sunday, a suicide car bombing killed 19 people at a Baghdad police academy.
Attacks against mostly Shia targets surged after Nouri al-Maliki's government moved against senior members of the Sunni-backed Iraqiya political bloc.
The prime minister's fragile coalition of Shia, Sunni and Kurdish factions is holding talks to ease the crisis, which has revived fears of a return to the sectarian strife seen in 2006-2007 when tens of thousands of Iraqis were killed.