(CNN) Philippines President Rodrigo Duterte ordered police officers in his country not to cooperate with United Nations human rights investigators and offered a crass warning to those conducting the probe.

"You're investigating us? Fact finding? Sorry, do not f*** with me," Duterte said Thursday, at an event before police officers and members of the military in his hometown of Davao City.

"Who are you to interfere in the way I would run my country? You know very well that we are being swallowed by drugs."

Duterte has long voiced opposition to international criticism to his so-called war on drugs, which has killed thousands in the less than two years since he took office. Last month , the International Criminal Court announced it was beginning a preliminary inquiry into the anti-drug campaign.

In his speech Thursday, Duterte warned soldiers and police officers in the audience of the possibility that their statements could be twisted and misconstrued for nefarious purposes.

"Once those human rights investigators or rapporteurs come, my order to you is: Do not answer. Do not bother," Duterte said during a speech Thursday, according to a translation from CNN Philippines

Duterte, previously mayor of Davao City, was elected after campaigning to aggressively combat drug users and dealers by any means necessary. Last year, the Philippines Dangerous Drugs Board estimated that the country had 1.8 million drug users, many of whom were methamphetamine users.

But the bloody nature of the crackdown has drawn the ire of advocates and international human rights authorities.

The Philippines government puts the figure much lower, estimating around 3,900 people have been killed in the drug war.

Duterte contends the issue is a domestic law enforcement matter and argues that international interference would constitute a violation of the Philippines' sovereignty.

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Presidential spokesman Harry Roque told reporters Tuesday that he'd recommend Duterte allow a special rapporteur to enter the country, but he said under no circumstances would it be the UN special rapporteur on extrajudicial, summary or arbitrary executions, Agnes Callamard.

Callamard has in the past condemned Duterte's drug crackdown.