The blast, which occurred at about 7.50am, also wounded 10 policemen and eight government employees, said police Captain Nabil Abdel Qadir.
The employees were just arriving for work at Iraq's oil ministry, irrigation ministry and national Police Academy, including some on a private bus that appeared to be damaged by the blast, Qadir said.
In Baghdad, the government working day usually begins at 8am.
Employees at the three government buildings affected by the blast are often searched at the checkpoint before they are allowed to walk to their offices about 100 yards away.
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