The Unification Ministry says North Korea's decision to shut down its main nuclear test site was a "voluntary" move it made ahead of the inter-Korean summit set for Friday.

Ministry spokesman Baik Tae-hyun told reporters Monday that the international community as well as the South Korean government believes the decision is a "significant development."

He noted that the North had dismantled its 20-meter cooling tower at its Yongbyon nuclear reactor complex three years after the joint statement on denuclearization was adopted at the six-party nuclear talks on September 19th, 2005.

However, Baik added that the Punggye-ri nuclear test site, where the North conducted six rounds of nuclear tests, is still available for use.

On the possibility of the upcoming summit touching on economic cooperation, Baik said the summit would focus on the denuclearization of the Korean Peninsula and the establishment of a peace system, as well as the sustainable development of South-North relations. 

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