The Philippines on Thursday called on the International Criminal Court not to resume its investigation into former president Rodrigo Duterte's deadly drug war, insisting the tribunal has no jurisdiction.

The appeal came on the day of ICC prosecutor Karim Khan's deadline for Manila to respond to his request to restart the probe into the anti-narcotics campaign that killed thousands of people.

Duterte pulled the Philippines out of the Hague-based tribunal in 2019 after it began a preliminary probe into the crackdown. His successor President Ferdinand Marcos has ruled out rejoining.

A government statement said the alleged murders did not amount to "crimes against humanity" and were being handled by the country's "proper agencies".

Last year, the ICC authorised a full investigation into the drug war, saying it appeared to be an illegitimate and systematic attack on civilians.

Rights groups say Duterte created a climate of impunity that led to an estimated tens of thousands of deaths at the hands of police, hitmen and vigilantes, even without proof that victims were involved in drugs.

The ICC, which only gets involved in prosecutions if member states are unable or unwilling to investigate, suspended the probe two months after Manila said it was looking into the alleged crimes.

Under pressure from the UN Human Rights Council and the ICC, the Duterte government began examining several hundred cases of drug operations that led to deaths.

Those efforts led to charges being filed in a handful of cases and the conviction of three police officers of wrongdoing.

Shortly before Duterte left office in June, Khan asked the court to restart the inquiry "as quickly as possible".

"With a handful of exceptions, the Philippine government has failed to provide any documentation to substantiate that the investigations are ongoing or complete, nor any details regarding concrete investigative or prosecutorial steps that have been taken," Khan said.

The UN Human Rights Council is expected to discuss the Philippines at its session starting next week, but rights groups have warned that drug war killings continue under Marcos.

"Our own monitoring and reporting on the Philippines shows that the situation is not improving since that last resolution," said Lucy McKernan, Deputy Director for the United Nations at Human Rights Watch, during an online briefing on Wednesday.

McKernan urged council members to "send a strong message" that Marcos, son and namesake of the late Philippine dictator, "does not have a clean slate to commit new abuses".