The victims have been identified as Al Mamun, 30, the owner of the ambulance, Milon Khan, 32, its driver, and Shimul, 30, an assistant.

The explosion occurred when one of the victims was removing the oxygen mask of a patient, sources said. 

Fortunately, the patient escaped unhurt.

The injured were taken to Sharankhola Upazila Health Complex and later shifted to Khulna Medical College and Hospital for better treatment, said Dr Farida Yeasmin, a doctor.

The victims sustained burn injuries in their hands and other parts of the body, she said.