Iraqi Shia militia leader Moqtada Sadr has said the US-backed security crackdown in Baghdad is doomed to fail.
A car bomb killed one person near the Iranian embassy
Mr Sadr said in a statement that no security plan would work unless Iraq's government assumed full responsibility for protecting its citizens.
His comments came as a series of bomb explosions hit Baghdad.
In one, at least 42 people were killed and 55 injured when a suicide bomber blew himself up at the entrance to a college in the east of the city.
Earlier, at least four people were hurt in a car bombing in the city's Karrada district, and one was killed in an explosion near the Iranian embassy.
The attacks came a day after Iraqi Prime Minister Nouri Maliki said sectarian killings had fallen as a result of the US-backed security surge.
Mr Sadr, whose militia controls the College of Administration and Economics, where most of Sunday's deaths occurred, once again called on the Americans to withdraw from Iraq.
Victims attending exams
Most of the victims of the blast at the college were students, police and witnesses said.
Many of the victims were young students
"There was an explosion. I did not feel anything for 15 minutes and when I returned to consciousness, I found myself in the hospital," Muhanad Nasir, a 22-year-old student, was quoted as saying by the Associated Press news agency.
Higher Education Minister Abed Dhiab al-Uljaili said most of the victims were students who had gone to sit exams and that five guards were among the dead, AFP news agency reported.
The agency said terrified parents converged on the scene, some collapsing in horror at the sight of blood and flesh at the entrance to the building.
The college is part of the al-Mustansiriyah university, Baghdad's second largest, and had received threats warning it to close, the BBC's Jane Peel in Baghdad says.
It is not the first time the university has been targeted.
Last month, more than 100 students were killed in a co-ordinated attack involving two car bombs and a suicide bomber at the university's main building.