Unionized firefighters have filed a complaint against interior minister Lee Sang-min as the ongoing investigation into the Itaewon crowd crush faces criticism that it is only focusing on frontline responders.

The firefighters' chapter under the Confederation of Korean Government Employees' Unions filed the complaint with the police’s special investigation headquarters on Monday, accusing Lee of causing death and injury by occupational and gross negligence and dereliction of duty.

The chapter urged the police to immediately open an investigation into the minister, who is tasked with overseeing the nation's disaster and safety management, while calling on him to take responsibility for the tragedy by stepping down.

It also called on the National Assembly to lead efforts to determine the exact cause of the tragedy.

The headquarters, which earlier said that it would expand the scope of its ongoing investigation, is currently conducting a legal review regarding the minister's authority to command police responses.