Deadly explosion at a Hanwha Aerospace facility is captured on a CCTV feed in this photo released June 24. Courtesy of DPK lawmaker Park Jung-hyun's office

Last month's deadly explosion at a Hanwha Aerospace facility in Daejeon appears to have occurred while cleaning a washing machine that may have contained explosive waste residue, police officials said Thursday.

The Daejeon Metropolitan Police Agency unveiled its initial assessment in a press briefing, citing a statement from a worker who was cleaning a tank within the washing machine at the time of the explosion on June 1 that left five workers killed and two others injured in the city located some 130 kilometers south of Seoul.

"I was cleaning a tank inside a washing machine at the time of the explosion. The blast seemed to originate from the machine," the worker was quoted as telling police.

According to the police, workers used chisel-like metallic scalers to remove waste residue accumulated on the washing machine, which, apparently, may have included explosive waste.