A lawyer representing the victims of former Philippine President Rodrigo Duterte 'war on drugs' on Friday (March 14) said the initial hearing at the International Criminal Court represented "a first step towards justice."

Duterte - who arrived in the Netherlands on a flight from Manila on Wednesday after being arrested on an ICC warrant on charges of crimes against humanity - sounded frail as he spoke via video link from a detention unit, confirming his name and date of birth for the court.

Defense attorney Salvador Medialdea said the former leader was too ill to say more, that Duterte's arrest and transfer to the Netherlands was "pure and simple kidnapping” and that his client was suffering from "debilitating" medical issues.

Presiding Judge Iulia Antoanella Motoc responded that the court doctor, who examined Duterte upon arrival, was of the opinion that he was "fully mentally aware and fit."

Prosecutors have accused the 79-year-old of carrying out a systematic attack on the civilian population during his time in office. Thousands of purported drug dealers and users were killed during a crackdown, when death squads he allegedly created and armed carried out widespread extrajudicial killings.