According to the head of the Musayib hospital in the nearby city of Hilla, among those killed on Saturday morning were three police officers. The explosion was caused by a booby-trapped car parked in front of the hospital, said Iraqi officials.
"Most of the victims are people who were heading to the hospital or to the headquarters of the local council," said Police Lieutenant Muhammad Tamimi.
Medical sources said some of the hospital's patients had heart attacks because of the explosion.
Speaking to Aljazeera, Iraqi journalist Talib al-Janabi said the hospital's doors and windows were broken and a number of cars were destroyed in the explosion.
Al-Janabi added that Iraqi police cordoned off the explosion site while US helicopters hovered over the area.
Musayib is a mixed Shia-Sunni town about 100km south of Baghdad.
Separately, a prominent Iraqi judge was assassinated by two fighters on a motorcycle in the southern port city of Basra, police said.
Taha al-Basri, a former chief judge at Basra's highest criminal court, was shot and killed on Saturday as he drove to work, said Lieutenant Colonel Karim al-Zaidi, an information officer at Basra's police headquarters.
Iraqi police are often targeted
by armed fighters
The judge's bodyguard was seriously wounded in the attack and was taken to a hospital, al-Zaidi said.
Also on Saturday, Iraqi police said they discovered the bodies of six men dressed in Iraqi National Guard uniforms dumped on a main highway near the northern city of Mosul.
The men had been shot in the chest and head, said Lieutenant Ali Husain from the Iraqi police. They were found in the area of Intisar, east of Mosul.
US soldiers die
Two US soldiers were killed in separate incidents while on patrols in Iraq, the US military announced early on Saturday.
A marine serving with the 1st Marine Expeditionary Force was killed on Friday while on a security operation in al-Anbar province west of Baghdad, said a military statement.
A soldier assigned to the same force was killed in a "non-hostile vehicle accident" in Babil province to the south of the capital.
The military said both incidents were being investigated, but no other details were given.
According to the latest US figures, 1457 US soldiers have been killed in Iraq since the US-led invasion in March 2003.