By Reuters

AMSTERDAM, Sept 15 (Reuters) - Judges at the International Criminal Court on Wednesday approved a formal investigation into possible crimes against humanity allegedly committed under the leadership of Philippine President Rodrigo Duterte in the context of his "war on drugs".

The ICC said in a statement that judges had approved a request by prosecutors to begin the investigation into potential murder as a crime against humanity.

Judges' assessment of material presented by prosecutors, was that "the so-called ‘war on drugs’ campaign cannot be seen as a legitimate law enforcement operation", but rather amounted to a systematic attack on civilians.

Human rights groups accuse Duterte of inciting deadly violence and say police have murdered unarmed drug suspects on a massive scale as part of the campaign. Police deny this, and Duterte says the police are under orders to kill only in self-defence. The government in Manila could not immediately be reached for a reaction late on Wednesday.