MANILA -- The Philippines is withdrawing from the International Criminal Court "effective immediately," President Rodrigo Duterte announced Wednesday.

In a statement, Duterte accused the ICC of violating his right to due process and presumption of innocence when a prosecutor with the tribunal announced the court was opening an investigation into Duterte's deadly war on drugs. Duterte complained that statements from United Nations officials showed they had already found him guilty.

"Given that the ICC shows a propensity for failing to give due respect to the State Parties of the Rome Statute, and that there is clear bias on the part of the U.N. against the Philippines, the Philippines may very well consider withdrawing from the Rome Statute," Duterte said in a statement, referring to the court's founding treaty.

Harry Roque, Duterte's spokesman, said the firebrand leader has instructed Executive Secretary Salvador Medialdea to notify the ICC of the Philippines' withdrawal.

Under ICC rules, a state's withdrawal takes effect one year after the international tribunal receives notification of its decision to leave.

ICC Prosecutor Fatou Bensouda, responding to a complaint from a Philippine lawyer, in February began a preliminary examination of Duterte's battle against drug traffickers. The campaign has led to thousands of deaths among suspected drug users and dealers.

Duterte insists the deaths have occurred as police acted in self-defense against suspected drug offenders. Last year, a 17-year-old youth was killed in a drug sweep when he allegedly drew a gun against the police. However, eyewitnesses and surveillance video suggested otherwise.

U.N. High Commissioner for Human Rights Zeid Ra'ad al-Hussein said Friday that Duterte needs to see a psychiatrist over his crude comments, including a threat to slap U.N. special rapporteur on extrajudicial killings Agnes Callamard, and the inclusion of U.N. special rapporteur on the rights of indigenous peoples Victoria Tauli-Corpuz on a list of alleged communist terrorists operating in the country.

Roque described al-Hussein's comments as a diplomatic affront to the Philippines.

Established in 1998, the ICC is tasked with prosecuting people accused of war crimes, genocide and other high crimes when domestic courts are unwilling or unable to investigate allegations or prosecute suspects.

The Philippines acceded to the ICC in 2011, becoming the 117th country to join the court.