A local source previously reported that three people had been killed and 45 more injured.
Earlier in the day, a Sputnik correspondent reported, citing local residents and officials that the blast had damaged the Zabul Provincial Hospital, which is located near the NDS regional office.
Zabul's Deputy Governor Malim Tawab said that the injured people had been taken to private hospitals and could be transferred to the city of Kandahar, if needed.
No terror group has claimed responsibility for the attack yet.
In August, one man was killed and three were injured in a bomb blast in the city of Jalalabad in the Afghan province of Nangarhar.
For almost two decades, Afghanistan has been dealing with instability due to a continuous insurgency by terrorist groups. Government forces conduct regular counterterrorism operations across the country.