North Korea appears to have increased operation of South Korean facilities at the Gaeseong Industrial Complex after Seoul's unification minister Kwon Young-se denounced the regime's illicit use of the infrastructure.

Voice of America(VOA) said Tuesday that according to satellite imagery taken on April 20, buses, personnel and materials were found at 21 buildings and other locations inside the complex.

The images show vehicles such as buses, provided by South Korea in the past, parked outside several plants as well as people's shadows and waste grounds filled with trash.

VOA said that given such circumstantial evidence, North Korea likely continues to illicitly operate the complex facilities. It also noted that it's the first time since 2016 when the business park shut down that active movement was captured on satellite photos.

The seemingly increased activity comes after a warning issued by the unification minister last month. He vowed to take legal action against Pyongyang's violation of South Korean property rights.

A ministry official told reporters on Tuesday that the government believes around ten or so factories at the complex are in operation and the number is likely to increase.