The International Criminal Court (ICC) is launching an official investigation into the alleged crimes against humanity in the Philippines under the leadership of President Rodrigo Duterte and his campaign against illegal drugs.

The Hague-based tribunal said Wednesday that it has authorized a probe into the allegations after it found a "reasonable basis" for the action. The ICC said a "specific legal element" had been met to prompt an investigation into crimes such as murder under Duterte's "war on drugs."

The ICC's pre-trial chamber found that Duterte's campaign was not a legitimate law enforcement operation as it resulted in the deaths of thousands. It added that while it is the government's duty to fight drug trafficking and addiction, the campaign's excesses made it illegitimate.

ICC Judges Péter Kovács, Reine Adélaïde Sophie Alapini-Gansou and María del Socorro Flores Liera all signed off on the order to launch a formal investigation. All of the judges reportedly reviewed all of the evidence presented before them on behalf of the 204 victims that came forward.

The judges reportedly found a "widespread and systematic attack against the civilian population" under the government's anti-drug campaign. They also found that law enforcement authorities had "failed to take meaningful steps" in their investigations and operations.

The latest request for an investigation into Duterte's drug war was submitted by former ICC prosecutor, Fatou Bensouda. In his request, which was submitted before his retirement in June, Bensouda alleged that the "war on drugs" had resulted in the deaths of thousands of suspected drug users and civilians.

Duterte has remained defiant and repeatedly defended his administration's actions. When Bensouda's request for an investigation was initially announced, Durterte reportedly shrugged it off and even threatened to "slap" the ICC magistrates.

In an interview Thursday, Duterte's legal counsel, Salvador Panelo, said the government will not cooperate with the investigation. Panelo said the Philippines will be closing its borders to ICC investigators.

Durterte's "war of drugs" was one of his main platform commitments before he became the country's president. During his campaign, Duterte had repeatedly urged police to "kill" all drug suspects.

As of the end of April 2021, police records showed that at least 6,117 suspected drug dealers had been killed during police operations. However, a report by the UN in June showed that the number could be as much as 8,600 deaths.