Which country is responsible for air-traffic control within its own territory?

Under the principles of international air law, every state possesses complete and exclusive sovereignty over the airspace above its territory, including its territorial sea.1

Because airspace is considered an appurtenance of the subjacent territory, each state is responsible for regulating the entry of foreign aircraft and maintaining authority over the activities within its own borders. Consequently, each nation holds the responsibility for managing air-traffic control and ensuring the enforcement of its laws within its sovereign airspace. While the International Civil Aviation Organization (ICAO) establishes international standards and recommended practices to ensure safety and efficiency, these regulations are designed to standardize aeronautical operations globally rather than replace the fundamental sovereign authority of individual states.123