Quetta: Four security officials have been martyred while 3 have been injured in blast near bomb disposal squad of security forces in Marget area of Quetta.According to security sources those who were martyred in the explosion are Subedar Shehzad Amin, Naib Subedar Abbas, Sepoy Khalil and Sepoy Zahid.The injured included Lance Naik Zafar, Lance Naik Farooq and Sepoy Khurram Saleem.Security Forces have cordoned off the area and started search operation.