Demolition work is underway at the site of the Seosomun Overpass collapse in Seodaemun District, in Seoul, Friday. Yonhap

Police on Sunday accelerated their probe into last week's deadly collapse of an overpass in central Seoul, focusing on whether the demolition work at the time of the accident was carried out in accordance with proper safety guidelines.

Last Tuesday, a section of the Seosomun Overpass in central Seoul undergoing demolition collapsed during an on-site safety inspection, killing three people and injuring three others.

The Seoul Metropolitan Police Agency has since launched an investigation into the case and raided the offices of the Seoul city government, an engineering company and others involved in the demolition.

On Sunday, police officials were reviewing materials seized in the raids to determine whether proper safety guidelines had been established and followed during the construction and demolition of the overpass.