The extremist group, also known as the Islamic State of Iraq and the Levant, obtained the location data from its own hacking group, named the "United Cyber Caliphate," the spy agency explained.

"While disseminating the location data of the installations and information on the individuals, (the group) incited (its sympathizers around the world) to retaliate for the benefit of Muslims," the NIS said.

Through the messaging program, the IS unveiled the locations of U.S. Air Force units in Pyeongtaek, Gyeonggi Province, and Gunsan, North Jeolla Province, and of one employee of a South Korean welfare organization.

The NIS said that it has told the U.S. Forces Korea and South Korean military and police agencies to fend off potential terrorist attacks against these targets and provide sufficient protection for them.

IS has repeatedly issued threats against a series of countries, including the U.S. and its ally South Korea.

In a video message released in November last year, IS presented the flags of 60 nations, including South Korea, casting them as members of an alliance against the militant group. 

Earlier this year, IS also issued a list of individuals that it said were against it, including 20 South Koreans.

In an effort to shield the nation against terrorist attacks, South Korean authorities have deported some 50 foreigners with links to terrorist organizations over the last five years. The authorities have also found two South Koreans who attempted to join terrorist entities.

"The government will make all-out efforts to protect the lives and properties of our citizens from terrorist threats while keeping close tabs on the movements of international terrorist groups," an NIS official said, declining to be named. (Yonhap)