Insurgents have killed at least 145 people and wounded 220 in a series of bombings, including at least three car bombs, in Baghdad's Shiite district of Sadr City, security and medical sources said.
One car bomb exploded at a market in Sadr City, a regular target for Sunni insurgents in the sectarian conflict that has killed thousands in Iraq.
Minutes before the blasts masked gunmen launched a daring raid on the health ministry, trapping about 2,000 people inside the building.
The explosions in Sadr City included three car bombs, the security source said.
He said one device went off at a market, a regular target for Sunni insurgents in the sectarian conflict that has killed thousands in Iraq.
In an audacious raid about 100 masked gunmen also attacked the health ministry in central Baghdad, clashing with guards and Iraqi army soldiers, deputy health minister Hakim al-Zamili told AFP.
He was trapped in the building with around 2,000 employees.
"First a series of mortars were fired at the building from the nearby Al-Fadhel neighborhood, and then about 100 masked gunmen holding machine guns attacked the building," said Zamili.
"About 2,000 employees are trapped in the building. I am also in the building," he added.
"The gunmen came in civilian cars and pick-up trucks and started shooting at the building and wounded a number of employees."
A security source said: "Fierce clashes are going on at this moment between the gunmen and guards of the building who are backed by Iraqi army soldiers."
"There are casualties but we do not have any details."
On Sunday gunmen kidnapped deputy health minister Ammar al-Assafar from his home in Baghdad's northern Adhamiyah district, while Zamili himself escaped an assassination bid on Monday.
Two of Zamili's guards were killed in the ambush.
'I condemn this shooting'
Insurgents have recently stepped up attacks against the government by targeting state-owned institutes and buildings.
On November 14 dozens of men wearing security forces uniforms assaulted a scientific research institute of the ministry of higher education and kidnapped around 150 people.
About 80 people, many of them employees of the ministry, are still believed to be hostages.
Sadr City, the impoverished district of followers loyal to radical Shiite cleric Moqtada al-Sadr, was also the site of an early morning incident involving US troops.
"US troops fired on a minibus carrying workers and killed a number of them in Al-Falah street at 6 a.m. today," Imam Abdel Zahra al-Suwaidi from the Sadr movement told AFP.
"I condemn this shooting that targeted the workers and accuse US forces of repeating such acts which leave many victims every day," Suwaidi said.
A medic at the Sadr City hospital said four people were killed and eight wounded, including two women.
An Iraqi security source also confirmed the incident.
"US forces fired on the minibus as the vehicle was seen on the streets before the dusk-to-dawn curfew was lifted," the source said.
But the US military said that Iraqi forces fired on the vehicle during a raid to detain the leader of a kidnapping cell.
"A vehicle displaying hostile intent was identified as an immediate threat to Iraqi forces. Iraqi forces fired on the vehicle to neutralise the threat," the military said without mentioning civilian casualties.
The security source said the workers were headed to a market in the Jamila neighbourhood near Sadr City at the time.