An online North Korean analytic site run by a U.S. think tank suggested construction of North Korea's Punggye-ri nuclear testing facility likely began nearly 40 years ago.

The contention was put forth in a post by "Beyond Parallel" under the Center for Strategic and International Studies(CSIS) on Tuesday, citing recently declassified satellite images by the Central Intelligence Agency(CIA).

The website showed two images from 1984 and 1987, the first by a KH-9 satellite under a CIA mission, and the second by the French SPOT 1 commercial satellite, narrowing down the probable timing for the commencement of construction to between 1985 and 1986.

The 1984 image showed numerous logging trails scattered throughout what would eventually become the northern test area of the Punggye-ri facility, but there was no evidence of facility construction or improvements to dirt roads.

In the 1987 image, an improved dirt road seemed to have been built leading to the entrance of what would later become known as Tunnel Number 1, along with significant tunnel excavation evidenced by a large spoil pile.

The image also suggested that excavation of Tunnel Number 2 had begun based on a tailings pile that would grow considerably over time, as well as construction of the Command Center Area some six kilometers south.

North Korea conducted its first nuclear test at the Punggye-ri site's Tunnel Number 1 on October 9, 2006, followed by five additional tests at Tunnel Number 2.