The International Criminal Court says the Philippines decision to leave the organization will have no effect on an on-going preliminary probe into possible crimes committed during Manila's war on drugs.

Last month, ICC prosecutor Fatou Bensouda, opened a preliminary examination into a complaint by a Filipino lawyer of suspected extrajudicial killings during President Rodrigo Duterte's anti-drug campaign, which could amount to crimes against humanity.

Last week, Duterte announced he was withdrawing the Philippine ratification of the Rome Statute, which created the ICC.

In its first reaction, the ICC said Tuesday it regretted Duterte's move, but stressed it would not affect Bensouda's preliminary examination.

It cited a decision in another case which said that the ICC retains jurisdiction over crimes committed when a country was an ICC member even after withdrawal.