More than 30 people were wounded, most of them seriously, said doctors at a hospital near the recruitment center in Taji, 12 miles north of Baghdad, The New York Times reported.
Some reports put the number of deaths higher, and accounts differed as to what caused the explosion.
A police official said a car bomb exploded in a parking lot near the center, while an Iraqi army source said a suicide bomber blew himself up in a crowd at the gate.
On Monday, a car bomb injured eight members of an army patrol in Taji.
In a separate incident Tuesday, one policeman was killed and two others were wounded when gunmen attacked a checkpoint in the Dora neighborhood of southern Baghdad.