Dozens of people have been killed and many more wounded in a series of blasts in the Iraqi capital, Baghdad.
At least 63 people died and 176 people were wounded in 12 bombings across the capital on Thursday morning, health ministry sources told Al Jazeera.
Two more bombs exploded in Baghdad late in the evening claiming two more lives, according to the Reuters news agency.
The wave of bombings come amid renewed fears of sectarian strife following the withdrawal of US troops and a deepening political crisis over an arrest warrant issued for Tariq al-Hashimi, the country's vice president and most senior Sunni politician.
The attacks largely coincided with the morning rush hour, and security forces cordoned off bomb sites, AFP news agency correspondents and officials said.
Live Box 20111212125010827866
Authorities believe the attacks were well co-ordinated, Al Jazeera's Omar al-Saleh said, reporting from Baghdad.
"We don't know who carried out the attacks, the Iraqi security officials did not identify any suspects yet," Saleh said, adding: "This I think is a major setback to the security forces on the ground who have a large presence in the capital. You have checkpoints, you have roadsblocks, and you have both the military and the Iraqi police guarding different areas, yet these attacks do occur."
Iraqi officials said the bombs struck in the Allawi, Bab al-Muatham and Karrada districts of central Baghdad, the Adhamiyah, Shuala and Shaab neighbourhoods in the north, Jadriyah in the east, Ghazaliyah in the west and al-Amil and Dura in the south.
Nouri al-Maliki, the Iraqi prime minister, vowed that the bombers would not be allowed to have any impact on the political process.
"The timing of these crimes and their locations confirm once again to any doubters the political nature of the goals that those criminals want to achieve," Maliki said in a statement.
The US condemned the bombings, and US vice president Joe Biden spoke with Iraqi President Jalal Talabani to voice support for his efforts to calm sectarian tension, the White House said.
"We continue to urge leaders to come together to face common challenges," Jay Carney, the White House press secretary.
"At this difficult time, the United States stands with Iraq as a strategic partner and a close friend," he said.
Nabil el-Araby, secretary general of the Arab League, has strongly condemned the attacks and called on all Iraqis, particularly members of the Iraqi government, to stay away from a partisan mindset.
'Planned and co-ordinated'
The largest explosion took place near the Rahbaat (Sisters) hospital and the Integrity and Transparency Directorate in Karrada district, sources told Al Jazeera.
"I saw all the windows were blown out and glass scattered everywhere. The children were scared and crying"
- Raghad Khalid,
The blast caused great material damage and the bodies of those killed were laid out in the streets, eyewitnesses said.
Will Geddes, a security specialist with International Corporate Protection, told Al Jazeera that "a number of potential motivations behind the attacks: It could be some means to destabilise the government and its credibility".
"It could also be message being sent out to the wider public in the international community to say that now that the US troops have left Iraq, this is a country which is still very much a security risk," he said.
"It is probably the worst co-ordinated attacks we have see in a significant period of time. The attacks were very planned and coordinated and would have required lot of resources.
"International community which has been very slowly engaging in Iraq for business opportunities may will need to sit back over the new year and certainly see what happens in the short-term if there would be more sustained attacks in the future."
"I saw all the windows were blown out and glass scattered everywhere. The children were scared and crying," said Raghad Khalid, a teacher at a kindergarten near the Karrada blast.
Smoke hung over the blast site in Karrada as ambulances rushed in to ferry the wounded to hospital.
Tensions between Iraq's Shia and Sunni communities have been heightened in recent days after Baghdad officials issued an arrest warrant for Hashimi over allegations that he ordered the killings of opponents.
Hashimi denies the charges and says they are politically motivated. Some Sunnis say the Iraqi prime minister is seeking to consolidate Shia control of the country following the departure last week of the remaining US troops stationed in the country.
"The fears of the people became reality," our correspondent in Baghdad said.
"I think the people are really scared and I think the politicians do know that their differences will be translated into attacks like these on the streets of Baghdad.
"From the official point of view, no one has come out yet saying there is a direct link, but among the general population they do have a fear and a genuine belief that attacks like this are a direct result of the differences between politicians," he added.
Source: Al Jazeera and agencies