(ATTN: UPDATES with USFK's comments in paras 10-11, other info in paras 5, 7, minor edits; CHANGES photo)

By Kim Seung-yeon

SEOUL, July 31 (Yonhap) -- A mix-up over a U.S. spy drone flying near the inter-Korean border has raised questions about a potential communication gap between the allies after South Korean forces mistook the drone for an enemy threat and had almost prepared to shoot it down.

On Thursday, the unmanned flying vehicle was spotted in the buffer zone, known as the Civilian Control Line, south of the Military Demarcation Line (MDL) separating the two Koreas.

The Army's 1st Corps, responsible for front-line defense, activated Durumi, an anti-air defense alert system issued in the event of an enemy drone incursion, and used surveillance equipment, including thermal observation devices (TOD) and radar, to identify the drone.

The South's Joint Chiefs of Staff (JCS) later said it was a U.S. military drone belonging to its Marine Corps carrying out an operation during a combined exercise with the South Korean Marines near the border.

The U.S. Forces Korea (USFK) said it was a drone operated by its Marines with the 3rd Battalion of the 7th Marine Regiment.

But questions have arisen over why the South Korean military was not aware of the allies' drone operation in the first place. The Army Ground Operations Command had reportedly mobilized its air defense assets, such as anti-aircraft artillery, to down the drone.

The USFK reportedly gave prior notice regarding its plan to operate drones near the border and coordinated the training with South Korean forces, but the South's military claims it never granted formal approval.

The JCS' readiness inspection office plans to visit the 1st Corps on Friday to investigate the overall situation regarding the drone incident, a JCS official told reporters.

"We will determine whether due procedures were properly followed, particularly regarding communication and coordination between the unit on the ground and the authority responsible for the final approval," the JCS official said.

The USFK said it is conducting its own investigation and reviewing the circumstances surrounding the incident.

"We are fully cooperating with the Republic of Korea military to establish the facts," it said, referring to South Korea by its official name.

The Chosun Ilbo daily reported Friday that the USFK informed the South Korean side of the plan to hold the drills and sent an official document regarding the drone operation, but it was never reported up the chain of command or shared with relevant units, citing unidentified military sources.

Under the South Korean military protocol, prior notification must be submitted to the Ground Operations Command for approval.

The combined Marine exercise took place at Story Firing Range, a U.S. live-fire training site in Paju near the Imjin River, just south of the MDL.

elly@yna.co.kr

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