A special police unit investigating the fatal Itaewon crowd crush has summoned the head of the security department of the Seoul Metropolitan Police Agency as a witness.

The unit called in Yoon Si-seung Thursday morning to clarify whether the Yongsan Police Station had requested additional support from the Seoul police ahead of the Halloween festivities.

Former Yongsan Police Chief Lee Im-jae has said that he twice requested additional forces from the Seoul Metropolitan Police Agency prior to Halloween, a claim refuted by the agency's chief, Kim Kwang-ho, who said no such request was received.

The special unit said earlier that a phone discussion was confirmed to have taken place between Kim and Yoon concurring that various factors made it difficult to deploy more police in the Itaewon area.

Meanwhile, more officials were called in for questioning on Thursday, including the chief of the Itaewon Police Station, who was summoned as a suspect to ask why the subway was allowed to stop at Itaewon station despite requests by the Yongsan police to close the station.