"I therefore declare and forthwith give notice ... that the Philippines is withdrawing its ratification of the Rome Statute effective immediately", Duterte said in a written statement explaining his decision to pull out of the statute that created the International Criminal Court (ICC).
Mr. Duterte said the ICC was "being utilised as a political tool against the Philippines" after its prosecutor "prematurely" announced a preliminary examination of allegations against him relating to killings amid his campaign against illegal drugs.
"Indeed it is a major foreign policy blunder that will take years to mend, if it can be mended at all", he added. The deaths occurring in the process of legitimate police operations lacked the intent to kill, ' he added.
Duterte has been threatening to pull out of the Hague-based global tribunal since the start of his presidential term in mid-2016.
Thousands of mostly poor drug suspects have been killed under Duterte's crackdown, but he has argued that the killings do not amount to crimes against humanity or genocide.
The statement, which had yet to be signed by Duterte, was given to reporters by presidential legal counsel Salvador Panelo, who confirmed to Reuters that the document was authentic.
The ICC is looking into the drug war after lawyer Jude Sabio filed a communication in April 2017. "The self-defence employed by the police officers when their lives became endangered by the violent resistance of the suspects is a justifying circumstance under our criminal law, hence, they do not incur criminal liability".
By withdrawing from the jurisdiction of the ICC, the president is following in the footsteps of Russia's President Vladimir Putin and also The Gambia, which cited racism against "people of colour, especially Africans" as a reason for leaving.More news: Under Analysts' Radar: Lexington Realty Trust (LXP)
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The President, however, bewailed that there was "fraud" in the country's ratification of the agreement, saying the Philippines was "made to believe" that the principle of complementarity, due process, and presumption of innocence, would prevail.
The outspoken leader, who is accused of stoking the killing of drug suspects with inflammatory statements, has fiercely pushed back since the Philippines became the first southeast Asian nation put under "preliminary examination" by the court's prosecutors.
Last Friday, the United Nations human rights chief, Zeid Ra'ad al-Hussein, suggested that Duterte "needs to submit himself to some sort of psychiatric evaluation" over his "unacceptable" remarks about some top human rights defenders.
In February, the ICC said it had started a preliminary examination to establish whether it had jurisdiction, and if crimes against humanity had been committed. "What it must do is to show that it is willing and able to bring all perpetrators of human rights violations to justice", it said.
Duterte has acknowledged his rough ways and tough approach to crime, but suggested many Filipinos have come to accept him.
Villarin also said that as a signatory to the Rome Statute and other treaty obligations, the decision of the President will be tantamount to reneging all other global commitments and obligations that would have unprecedented repercussions to the country's worldwide standing as a sovereign state.
"This is a penal law, and should be published pursuant to the ruling of the Supreme Court.What the Court says is the provisions of a penal law be published so the people will know exactly what is being punished by the treaty", Roque said.
Villarin said it could also embolden China, which has refused to comply with an global arbitration ruling that invalidated its vast territorial claims in the South China Sea.