BANGKOK, Oct. 20 -- Thai authorities have launched an investigation into a series of illegal developments on Koh Phangan after several buildings were found inside a protected national forest reserve, raising alarm over alleged foreign-backed nominee businesses accused of degrading the island's environment.

According to Khaosod English, a task force tackling land encroachment and environmental crimes in the Fourth Army Region revealed on Saturday that inspections conducted in September uncovered extensive forest damage.

Aerial photography and GPS mapping showed at least five buildings built inside the national forest reserve, in violation of the National Forest Reserve Act of 1964.

Cleared and graded hillsides, newly drilled groundwater...