North Korea has reportedly expressed its concern over some of the infrastructure at the Gaeseong Industrial Park having the potential to be used for spying by South Korea.

The North ended its two-day probe of the complex Tuesday.

According to the South Korean Unification Ministry, North Korean officials from the National Defense Commission raised the possibility that the 15-story-high support center and the 70-meter-high water treatment tower may be used to spy on the North Korean military’s guard posts and the movement of North Korean guards near the industrial complex.

The North Koreans also took issue with South Korean publications and DVDs which South Korean workers bring to the inter-Korean joint industrial park.