A car bomb has exploded near two government offices in central Baghdad, killing at least 13 people and wounding more than 50.
Two police officials say the car was parked near an office for Shiite Muslim religious affairs and the city's health department in the Bab al-Muadham area.
The explosion at 11am local time damaged nearby buildings and cars.
A doctor in a nearby hospital confirmed the casualty figures.
The powerful car bomb tore the facade off of Iraq's main religious affairs office for Shiite Muslims and the death toll was raised to at least 18 - making it the deadliest single attack in the capital in three months.
The blast came at a time of prolonged political paralysis in Iraq caused by sectarian tensions. It followed a series of attacks that killed 17 people in Baghdad last week.
Adel Ahmed, an employee at the nearby Baghdad Health Department, said he was reading a newspaper in his office when he heard the blast.
"The ceiling fell on my head and I was slightly wounded in the head and fell down," he said. He added that he walked to the scene of the explosion and saw wounded people on the ground screaming for help. "The scene was horrific," he said.
Two police officials said the explosives-rigged car was parked near the religious affairs building and the health department. The front of the three-story religious affairs office collapsed from the impact of the blast.
Firefighters were searching the debris for survivors. The blast also shattered nearby windows and damaged cars in the area.
The damaged building housed the so-called Shiite endowment, or department that supervises Shiite religious affairs, including holy sites and mosques across Iraq.
Violence has fallen in Iraq since a wave of sectarian bloodshed in 2006 and 2007, but insurgents carry out frequent attacks on security forces and civilians to undermine the Shiite-led government following the pullout of US forces in December.
A unity government headed by prime minister Nouri al-Maliki, a Shiite, has been largely paralysed since the withdrawal of the US troops.
There is mounting criticism of Mr al-Maliki within the ruling coalition, over complaints that he is shutting out Iraq's two main minorities - Kurds and Sunni Muslims - in decision-making. However, his opponents appear to fall short of a needed majority in parliament to bring down him down.