The blast was so powerful it nearly vaporized the suicide bomber's car, leaving only its engine partially intact, the Associated Press reported.
Body parts and pools of blood scattered the street outside the clinic in Hillah, a predominantly Shiite area about 60 miles south of Baghdad. The injured were piled into pickup trucks and taken to nearby hospitals.
Dia Mohammed, the director of Hillah General Hospital, said most of the 115 dead and 133 wounded were recruits waiting to take physicals as part of the application process to join the Iraqi police and national guard, reported the AP.
"I was lined up near the medical center, waiting for my turn for the medical exam in order to apply for work in the police," said Abdullah Salih, 22. "Suddenly, I heard a very big explosion. I was thrown several meters away and I had burns in my legs and hands, then I was taken to the hospital."
"I was lucky because I was the last person in line when the explosion took place," said Muhsin Hadi, 29, a recruit, whose leg was broken from the blast. "Suddenly there was panic, and many frightened people stepped on me. I lost consciousness and the next thing I was aware of was being in the hospital."
Babil province police headquarters said "several people" were arrested in connection with the blast. Insurgents have repeatedly targeted security recruits.
The deadliest previous single attack occurred Aug. 29, 2003 when a car bomb exploded outside a mosque in Najaf, killing more than 85 people, including Shiite leader Ayatollah Mohammed Baqir al-Hakim.
A second car bomb exploded Monday at a police checkpoint in Musayyib, about 20 miles north of Hillah, killing one policeman and wounding several others, according to a police source, the AP reported.
Meanwhile, Iraqi officials said Sunday that Syria had captured Saddam Hussein's half-brother, a most-wanted leader in the Sunni-based insurgency.
Sabawi Ibrahim al-Hassan, who shared a mother with Saddam, was nabbed along with 29 other fugitive members of the former dictator's Baath Party in Hasakah in northeastern Syria, 30 miles from the Iraqi border, the officials said on condition of anonymity, reported the AP. The U.S. military in Iraq had no immediate comment.