World Bulletin / News Desk
Another officer was unaccounted for and two more were injured following the incident, which happened while repairs were being carried out on a submarine off the country's southeastern coast.
The missing officer had reportedly been working on top of the submarine when he was thrown into the water.
Navy officials cited by local news agency Yonhap suspected a gas explosion was responsible.
North Korea has issued a series of threats this year to attack the South and its ally the United States -- although physical clashes between the two sides in recent years have been restricted to the border area hundreds of kilometers (miles) north of the accident site.
South Korea is planning to bolster its defenses in the coming months, including by deploying a contentious American anti-missile system known as THAAD (Terminal High Altitude Area Defense).
Against the backdrop of ongoing tensions, Seoul's defense ministry also confirmed that U.S. Army chief of staff Gen. Mark A. Milley will arrive in the South this Wednesday for a three-day visit.