THE HAGUE, Netherlands - The International Criminal Court said Thursday it had authorised the reopening of an inquiry into the brutal anti-drugs campaign by former Philippines' president Rodrigo Duterte which left thousands dead.

Duterte pulled the Philippines out of the Hague-based tribunal in 2019, a year after the ICC began a preliminary probe into the crackdown.

The ICC then launched a formal inquiry in September 2021, only to suspend it two months later after Manila said it was re-examining several hundred cases of drug operations that led to deaths at the hands of police, hitmen and vigilantes.

Officially, 6,181 people were killed in Duterte's "war on drugs" but rights group say that up to 30,000 may have been killed, some innocent victims, and that corruption was rife among security forces that acted with impunity.

ICC prosecutor Karim Khan asked to restart the inquiry in June 2022, saying the Philippine government under Duterte's successor, President Ferdinand Marcos, had not provided enough evidence it was carrying out thorough inquiries.

In a statement Thursday, the ICC said its pre-trial chamber "is not satisfied that the Philippines is undertaking relevant investigations that would warrant a deferral of the court's investigations".

"The various domestic initiatives and proceedings, assessed collectively, do not amount to tangible, concrete and progressive investigative steps," it added.

Marcos has vowed to continue the drug war but with a focus on prevention and rehabilitation, though so far he has ruled out rejoining the ICC.

In November, a Philippine police officer was jailed for planting evidence and torturing two teenagers killed at the height of Duterte's drug war, a rare conviction of an enforcer of the crackdown.