But in a 15-page statement, dated March 13, Duterte said he was withdrawing from the ICC's founding treaty, the Rome Statute, because of "baseless, unprecedented and outrageous attacks" by United Nations officials, and ICC actions that he said failed to follow due process and presumption of innocence.
"I would like to address myself to the International Court of Justice and to the prosecutors coming here to investigate: the war or the drive against drugs will not stop and it will last until the day I step out".
The decision was reached, as the firebrand President took a swipe at the UN's alleged attempt to depict him as "ruthless and heartless violator of human rights", and the ICC's plan to have jurisdiction over him.
The ICC can only intervene in a member state when that state is unable or unwilling to carry out investigations and prosecute suspected perpetrators.
They allege that Duterte's drug war represented a systematic, state-sanctioned act of violence against a specific group, namely suspected drug dealers and users, in violation of due process, basic principles of human rights and worldwide humanitarian law.
Through the note, the Philippines gave its assurance to the worldwide community that it continues to be guided by the rule of law embodied in the country's Constitution and its long-standing tradition of upholding human rights.
Quitting the court requires a year's notice and experts say pulling out does not preclude an investigation of the killings, which have drawn global concern.
Mr Duterte's chief legal counsel, Mr Salvador Panelo, said the president was "definitely not afraid" of an investigation from The Hague court.
According to global law, Duterte and the Philippines are under the jurisdiction of the ICC as a result of being a member of the court, and withdrawing would not change that jurisdiction retroactively.More news: Avengers: Infinity War Trailer
Presidential spokesman Harry Roque cautioned that there might be an "avalanche" of countries leaving the ICC while other nations are likely to refuse to join the worldwide court now.
The Philippines ratified the treaty in 2011, which means the court has jurisdiction for crimes within its mandate committed from that year.
Duterte, who is buoyed by high popularity ratings at home, has fiercely defended the drug war as a battle to bring safety to the nation's 100 million people.
He said the withdrawal was not a way to evade an ICC investigation. The ICC has only publicly indicted 41 people from thousands of complaints since its inception in 2002.
Duterte has insisted that the ICC has no jurisdiction over him.
Roque argued that the Rome Statute that set up the ICC has "no universal ratification", explaining that only 124 out of 168 countries signed the Rome Statute that set up the ICC.
Should the Philippines withdraw from the court it would not be the first to do so, as Burundi became the first nation to leave in October 2017. ICC conducted the probe in response to a communication filed by Atty.
Under Article 127 of the Rome Statute, a state party's withdrawal from the treaty can only take effect a year after the written notification is received by the UN Secretary-General.
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