Seoul's foreign ministry released the declassified documents on Tuesday.
According to the dossier from 1986, Korea concentrated its diplomatic efforts on dealing with China, well before international ties between the People's Republic of China and South Korea were formally established in 1992.
Korea and the U.S. pushed through a secret plan, code-named "Moran Gusang" or the "Peony Project," to simultaneously normalize relations between Seoul and Beijing, and Washington and Pyongyang, to alleviate the tensions on the Korean Peninsula.
The plan was devised to keep tabs on the strengthening ties between North Korea and the Soviet Union at the time,. and as China, which was also becoming less at ease due to the Soviet Union introducing a variety of new weapons to Pyongyang in the mid-80s, tried to expand its influence over the peninsula.
The 230,page dossier also revealed that Seoul acknowledged North Korea's alleged involvement in the murder of a daughter of a judge who issued a sentence of the death penalty to those responsible for the Rangoon bombing.
The Rangoon bombing was the 1983 assassination attempt on then-President Chun Doo-hwan, orchestrated by North Korea, which killed 21 people, mostly officials, and wounded 46 others.
According to the dossier, Chun apparently tried to reduce the commemorative ceremonies, even with Soviet fighters shooting down a Korean jet in the same year, under the pretext of inter-Korean dialogue and a successful Seoul Olympics slated for 1988.
The document also revealed that Chun expressed his regret to the visiting U.S. secretary of state for his previous public pledge that he wouldn't seek a second term in accordance with the Constitution, which permitted only a single seven-year presidential term.
The declassified documents have been made public, as the retention period for classified documents in Korea is 30 years.
The original documents can be read at the Diplomatic Archives in southern Seoul.
Hwang Hojun, Arirang News.