Former Philippine President Rodrigo Duterte was "abducted" before being taken to The Hague to face murder allegations and is too ill to give evidence, his lawyer told the International Criminal Court at his initial appearance on Friday.

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 and former Palace executive secretary 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.

Duterte arrived at Rotterdam airport on a chartered plane Wednesday and was transferred to a detention unit on the Dutch coast up the road from the ICC building. In a video message on social media, he took responsibility for his actions.

During the initial appearance, the judge summarized the allegations against Duterte, who was not asked to enter a plea.

Rodrigo Duterte makes first ICC appearance

Duterte, who led the Philippines from 2016 to 2022, is set to be the first Asian former head of state to go on trial at the ICC, a court of last resort created more than two decades ago to prosecute individuals for war crimes, crimes against humanity, aggression and genocide.

Duterte has said that he suffers from a series of ailments including a chronic neuromuscular disorder, back problems, migraines and a condition that can cause blockages in the blood vessels.

Duterte's surrender to the court marks a big victory for Chief Prosecutor Karim Khan, who faces U.S. sanctions over his arrest warrant for Israeli Prime Minister Benjamin Netanyahu.