The injured were cashier Sanjay Ganapati (30) and salesman Nurul Islam (25). Nurul was admitted to the Sylhet Osmani Medical College with serious injuries.
Sources said that two of the attackers came on a motorcycle to Shawquat Traders in Shibganj wanting to buy fuel 30 minutes before the incident.
They were enraged by Nurul who apparently touched the leg of one of the attackers, Zakaria, when re-fueling the motorcycle.
The petrol pump authorities tried to settle the issue by apologising, but the men left the scene and came back and attacked the petrol pump.
Eyewitnesses said 12 BCL activists launched the attack at around 9pm. They looted around TK 45,000 from the cashbox, after ransacking the windowpanes of the pump and beating up its two employees.