The attack was carried out by a suicide car bomber last night, according to police and hospital officials who spoke on condition of anonymity in line with regulations. They put the death toll at four.
But Saad Mann, a spokesman for the Interior Ministry and Baghdad Operations Command, told the Associated Press that only three were killed in the bombing. He said all those killed were policemen and did not offer any information as to the number of injured.
The differing accounts could not be immediately reconciled. The explosion targeted an entrance to the traffic police station in Baghdad's Karrada neighbourhood. Moments after the attack the burning shell of a car could be seen sending up a plume of thick black smoke as police fired into the air to disperse a small crowd.
The attack comes as Iraqi forces struggle to push back Islamic State group militants in the northern Iraqi city of Mosul, the last pocket of significant urban territory the group holds in Iraq.
IS has carried out similar attacks targeting Iraqi security forces in the past. Iraqi and coalition officials have warned that as IS loses ground in Iraq the group will increasingly return to its insurgent roots.
In July of last year a massive truck bombing in the same Baghdad neighbourhood killed more than 300 people on a busy street lined with shopping malls. The attack was the deadliest single bombing in Baghdad since US-led forces toppled Saddam Hussein in 2003.