Osan Air Base in South Korea was locked down Monday because of reports of an active shooter at a high school on the grounds of the U.S. base, military officials said.


People on the base have been told to stay in their quarters or workplaces until further notice, according to Tech. Sgt. Stacy Foster, a spokesman at Osan. He had no other details. Another official confirmed the lockdown and reports of a shooter but also had no further details.


Osan Air Base is located south of Seoul. It is home to some of the 28,500 troops stationed in South Korea as a deterrent to North Korea, whose 1950 attack started the Korean War.


Osan's 51st Fighter Wing posted on its official Facebook site that a perimeter had been established and security forces had swept half of all three buildings in the area but had no reports yet of suspicious activity.


The presence of the U.S. troops and annual U.S.-South Korean war drills are a continuing point of contention with North Korea, which claims that they are signs of hostility and designs at invading the North.