U.S. Air Base in South Korea Under Lockdown Amid Reports of Active Shooter at Base High School (UPDATE: Lockdown Lifted; Precaution After Unscheduled 'Shooter Drill,' Principal Says)

UPDATE 10:15 p.m.: SEOUL, South Korea (TheBlaze/AP) - U.S. base lockdown was a precaution after unscheduled "shooter drill," principal said. Stars and Stripes confirmed the lockdown was precautionary and is now lifted.

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UPDATE 10:07 p.m.: SEOUL, South Korea (TheBlaze/AP) — 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. 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.

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A United States air base in Seoul, South Korea, was under lockdown Monday morning amid reports of an active shooter at the school there, the Associated Press reported.

Security forces have responded to the incident at Osan Air Base, wing spokesman 1st Lieutenant Brandon Baccam told Stars and Stripes.

Photo of Osan Air Base, Republic of Korea, taken Oct. 17, 2014. (Image source: Osan Air Base website/Senior Airman Matthew Lancaster)

More from Stars and Stripes:

Several security forces personnel and vehicles were spotted around 11:15 a.m. at the base’s middle school and high school. The base was otherwise deserted as the season's first snow flurries fell, with a loudspeaker repeating the same message every few minutes in both English and Korean: “Lockdown, lockdown, lockdown. Seek safety and shelter.”

A post on the wing’s Facebook page just before 11:20 said that due to reports of a possible active shooter, a perimeter had been established and security forces were sweeping the area, with a 50 percent sweep of three buildings completed. The buildings were not identified.

“At this time, there have been no reports of suspicious activity reported,” the post said.

The 51st Security Forces Squadron practiced responding to a live shooting situation in mid-November, using Osan Middle School as the setting for a mock shooting. Responders practiced clearing the building and used rubber bullets during the exercise to make sure there were no injuries, according to the wing’s website.

This is breaking news; updates will be added.