Hanwha Aerospace's Daejeon business site in Yuseong-gu, Daejeon, on Monday, after a fatal explosion at the facility. Access to the area around the main gate was restricted following the accident. (Yonhap) Hanwha Group and its defense arm Hanwha Aerospace apologized Monday after a deadly explosion at the company's Daejeon facility killed five workers, pledging full cooperation with authorities and a thorough investigation into the cause of the accident.In a joint statement, the companies said they were “deeply saddened and devastated” by the loss of five workers in the accident that occurred earlier in the day at Hanwha Aerospace’s Daejeon plant in Yuseong-gu.“We offer our deepest condolences to the deceased employees and sincere sympathy to their bereaved families,” the companies said in a statement. “We bow our heads in apology to the Korean people.”The company said it would provide all necessary support for injured employees and their medical treatment.Daejeon fire authorities reported receiving approximately 30 calls at around 10:59 a.m. Monday from people reporting hearing a loud explosion and seeing smoke rising from the site. The explosion left five dead and two injured, who are currently under treatment. Firefighters were able to fully extinguish the blaze by 1 p.m.The exact cause is not yet known, but authorities suspect that rocket propellant may have exploded.Following the accident, Hanwha Aerospace CEO Son Jae-il convened an emergency response meeting at the company’s Seoul headquarters and traveled to the accident site in Daejeon.The company said it had established an emergency task force on-site and is working closely with fire authorities, police and other government agencies to contain the situation and determine the exact cause of the explosion."We will thoroughly identify the cause of the accident and take every necessary measure to ensure such a tragic incident never happens again," the company said.The Daejeon facility is one of Hanwha Aerospace's key aerospace and defense research and production sites. At the site, the company develops and produces large-scale propulsion systems and tactical surface-to-surface weapon systems, handling propellant mixing and loading operations.The site is involved in the development of propulsion systems for weapons such as multiple-launch rocket systems and missiles, requiring the handling of highly sensitive combustible and explosive compounds. These materials can ignite or detonate when exposed to shock, friction or heat.The accident marks the latest in a series of fatal incidents at the Daejeon facility.In May 2018, an explosion at the site killed two workers at the scene, while three others later died from injuries sustained in the accident. In February 2019, another explosion occurred in a propellant processing facility, killing three workers.