At least four persons were injured when a blast occurred in a shop of a petrol pump here on Monday. According to details, the blast occurred in a mini mart at a petrol pump in Khayaban-e-Ittehad area of Defence Housing Authority (DHA). Heavy contingent of police and Rangers reached the spot and cordoned off the area after the incident. The injured were shifted to a hospital for treatment where according to hospital sources their condition was termed as stable. Meanwhile, the nature and intensity of the explosion could not be ascertained until the filing of this report.