Four men, including two Chinese nationals, were released on Thursday after investigation after they were initially arrested for using a drone to make videos of the newly constructed Islamabad International Airport. The drone was also shot down, sources within the Airport Security Force (ASF) said.

ASF sources said the arrested men were workers of a Chinese company involved in construction of the airport and were making the drone footage without permission. They later added that the arrested men had taken permission from the Civil Aviation Authority (CAA) to use the drone to make videos before ASF took charge of the airport's security and the force was not aware of it when the drone was shot down.

The drone, damaged as a result of firing, was also confiscated by ASF officials.

Meanwhile, the employer of the arrested individuals has claimed that the video was to be used as proof of the work that has been completed by them.

Following a number of controversies and delays, the new airport — built on the outskirts of federal capital — is now set to begin flight operations from May 3. The first test flight landed at the airport earlier this month.

In its initial phase, the airport will be capable of handling nine million passengers and 50,000 tonnes of cargo every year. After its expansion, it would be able to serve up to 25m passengers a year by 2025, authorities say.