The injury figure in the blast was earlier put at 14 by ER CPRO R N Mahapatra.
The blast took place at 3.55 AM as soon as the train left Titagarh station in the northern fringes of the city.
Six of the injured have been admitted to B R Singh Railway hospital here. Of them, four have serious injuries, a press release issued by ER said.
Quoting doctors of the hospital, it said that their condition is stable.
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R K Gupta, ER general manager who visited the spot, said it was an incident of gang war.
Gupta, who also inspected the compartment, said there was no damage to the coach due to the blast.
"But forensic experts will come and inspect the coach," he said.
He asked passengers to be alert and cooperate with railways authorities to help strengthen passenger safety.
Security has been beefed up to ensure passenger safety, Mohapatra said.
The rake was brought back to Sealdah carshed and normal train services resumed on the up line within an hour of the incident after security clearance. There was no disruption of train services in the down line, an ER release said.