Chamnan Chanruang, the Chiang Mai-based former chairman of Amnesty International Thailand, said his call especially related to CCTV recordings of the incident in Chiang Dao district last Friday.

Third Army Area 3 chief Lt-General Wijak Banpasop claimed the recordings showed 17-year-old Chaiyapoom resisting soldiers in the performance of their duty.

Chamnan said the probe was necessary to determine if the officers over-reacted.

He said the case had attracted massive attention locally and internationally, so transparency was key.

The Army said the killing of Chaiyapoom was an act of self-defence after the teen allegedly pulled out a knife and a hand grenade.

The Army described him as a suspected drug trafficker, alleging 800 methamphetamine tablets were found in his car following the shooting.

In response to the drug dealing allegation, Chamnan said the case should be investigated fairly based on available evidence.