Manila, Philippines - Former Philippines president Rodrigo Duterte was arrested Tuesday in Manila by police acting on an International Criminal Court warrant tied to his deadly war on drugs.

The 79-year-old faces a charge of "the crime against humanity of murder," according to the ICC, for a crackdown that rights groups estimate killed tens of thousands of mostly poor men, often without proof they were linked to drugs.

"Early in the morning, Interpol Manila received the official copy of the warrant of the arrest from the ICC," the presidential palace said in a statement.

"As of now, he is under the custody of authorities."

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The statement added that "the former president and his group are in good health and are being checked by government doctors."

Duterte's former chief legal counsel, Salvador Panelo, called the arrest "unlawful."

"The (Philippine National Police) didn’t allow one of his lawyers to meet him at the airport and to question the legal basis for PRRD's arrest," he said, adding a hard copy of the ICC warrant had not been provided.

But a group that worked to support mothers of those killed in Duterte's drugs crackdown called the arrest a "very welcome development."

"The mothers whose husbands and children were killed because of the drug war are very happy because they have been waiting for this for a very long time," Rubilyn Litao, coordinator for Rise Up for Life and for Rights, told AFP.

Human Rights Watch, meanwhile, called on the government of President Ferdinand Marcos to "swiftly surrender (Duterte) to the ICC", saying the arrest was a "critical step for accountability in the Philippines".

Duterte's Tuesday morning detainment at Manila's international airport followed a brief trip to Hong Kong.

Speaking to thousands of overseas Filipino workers there Sunday, the former president decried the investigation, labelling ICC investigators "sons of w*****" while saying he would "accept it" if an arrest were to be his fate.

The Philippines quit the ICC in 2019 on Duterte's instructions, but the tribunal maintained it had jurisdiction over killings before the pullout, as well as killings in the southern city of Davao when Duterte was mayor, years before he became president.

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It 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.

The case resumed in July 2023 after a five-judge panel rejected the Philippines' objection that the court lacked jurisdiction.

Since then, the Marcos government has on numerous instances said it would not cooperate with the investigation.

Duterte, who is still hugely popular among many in the Philippines who supported his brutal "solutions", is running to reclaim his job as mayor of his stronghold Davao in May's mid-term election.

Charges have been filed locally in a handful of cases related to drug operations that led to deaths, but only nine police have been convicted for slaying alleged drug suspects.

A self-professed killer, Duterte instructed police to fatally shoot suspects if their lives were at risk.

At the opening of a Philippine Senate probe into the drug war in October, Duterte said he offered "no apologies, no excuses" for his actions.

"I did what I had to do, and whether or not you believe it or not, I did it for my country," he said.