A South Korean soldier who suffered bullying has killed eight of his comrades and injured two others.
The incident happened near the border with North Korea
The 22-year-old soldier, identified as Kim Dong-min, threw a grenade and then fired at fellow soldiers while they slept, the defence ministry said.
The incident took place in Yeoncheon county near the heavily-militarised border with North Korea.
A spokesman said Private Kim had suffered "verbal violence and molesting" from a senior officer.
The soldier's platoon commander was among those killed in the attack.
Five of the soldiers are reported to have died in the initial grenade blast.
The remaining three are said to have been killed when Mr Kim took a rifle from a fellow soldier and opened fire, using up to 40 rounds of ammunition.
Two soldiers being treated for their injuries are expected to survive, a spokesman said.
Military under pressure
The conscript was a university student before beginning his two years of military service last December.
He was returning from an overnight patrol in the early hours of Sunday, when he attacked the soldiers who were sleeping at a guard post.
The defence minister apologised for the incident
The unit was stationed close to the demilitarised zone, the stretch of no-man's land that divides North and South Korea.
Defence Minister Yoon Kwang-ung has called an emergency meeting in response to the incident.
He apologised and vowed to take necessary steps to prevent any repetition.
Chang Suk-kyu, a chief spokesman for the defence ministry said Private Kim had "suffered verbal violence and molesting from his senior".
The BBC's Charles Scanlon says there are frequent reports of bullying and violence against conscripts in South Korea's 600,000-man army.
The military is already under pressure following the infiltration of an unarmed North Korean soldier through the demilitarised zone last week.
There has been no explanation as to how he got through it without being detected.