An officer in South Korea's army opened fire on his troops, killing five and injuring many more, an army official said. The incident comes amid high tension between the two Koreas.

The army sergeant opened fire with his rifle Saturday evening in Gangwon province, east of Seoul, a Ministry of Defense official told media on condition of anonymity, citing rules that prevent him from speaking with the media. Local South Korean media report the officer is at large, but the government has not confirmed this.

Though North Korea is not believed to be involved in the incident, tensions remain high between the two countries, with the north orchestrating military drills and threatening South Korea's president.

The Associated Press reports that the Korean border is one of the most militarized in the world. This is because North and South Korea in 1953 signed an armistice, not a peace treaty, meaning the nations have technically been at war since then. Because of this, South Korean men must serve two years in the military.

Border shootings have occurred a few times: In 2011, a soldier went on a rampage at his base in Gwanghwa Island, and in 2005, another soldier threw a grenade and opened fire on his unit because he was upset by the verbal abuse of his superiors.

Though defending the nation from communist invasion was once seen as an honor, many young South Koreans do not see the need to be part of the military since no actual fighting has happened in 60 years. They resent the interruption of military service, as well as being part of the hierarchical and strict organization.

The New York Times reported three years ago that superiors once used corporal punishment to curtail insubordination but that some people believed the approach needed to be changed.