The blast happened at around 7:00 pm (1600 GMT) in the busy business district of Hay al-Amel in the west of the city, he said.
There was no immediate claim of responsibility for the explosion, which bore all the hallmarks of a suicide attack by the Islamic State group.
The radical Sunni militant group is under assault in both Iraq -- in the country's second city Mosul which IS seized in June 2014 -- and in neighbouring Syria.
Iraqi forces fight IS in Mosul as bomb blasts hit Tikrit wedding
In that year, the militant took vast swathes of Iraqi territory north and west of the capital.
Iraqi government forces backed by the US-led international coalition have since retaken many cities, including Tikrit.
But as IS has lost ground in Iraq, it has also retained the ability to stage regular attacks there.
COMMENTS
Comments are moderated and generally will be posted if they are on-topic and not abusive.
For more information, please see our Comments FAQ