A sticky bomb attached to a civilian vehicle detonated around 7:33am in Dogh Abad area of the capital, said police spokesman Ferdaws Faramarz.
Initial reports indicated it killed at least one civilian.
The police spokesman later put the toll of the dead to five, including four medical doctors working for Pul-e Charkhi prison.
Another two people were wounded in the bomb attack, he added.
There was no immediate claim of responsibility.
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