MANILA, Feb. 2 (Xinhua) -- Philippine President Rodrigo Duterte said on Thursday that he would soon issue an order that would authorize the Armed Forces of the Philippines (AFP) to help in the war against drugs.

"I still have to write the executive order, but I have taken in the AFP and raised the issue of drugs as a national security threat, so that they can call (on) the armed forces to assist," Duterte said in a speech in Davao City.

He promised on Thursday that there will be no let-up in his anti-drug campaign and threatened to "kill more" drug suspects.

"I will kill more, if only to get rid of drugs," he said.

Duterte has temporarily halted his drug war while he is cleansing the country's police force after earning criticisms from international human rights groups, ordering the military to help in the process.

He said he would also strip the National Bureau of investigation the power to enforce his drug war.

"I've lost my trust in you," he said.

He has said the Philippine Drug Enforcement Agency and military can go after the drug suspects for the time being.

"In the meantime, there will be a purge inside Camp Crame," he said, referring to the main headquarters of the Philippine National Police.

Duterte ordered the military on Tuesday to arrest rogue policemen, especially those who are allegedly in cahoots with drug lords, in the wake of reports that some policemen are using his anti-drug campaign to commit wrongdoings.

Duterte gave the order in the wake of discovery that active policemen are involved in the kidnapping of a South Korean businessmen in October last year. The South Korean was eventually killed but the kidnappers demanded millions of pesos in cash from the victim's family.

Duterte's defense secretary Delfin Lorenzana on Tuesday requested Duterte's office "to issue an official order regarding the presidential directive to serve as a legal basis for our troops to follow."

"By the same token, the president's verbal directive to arrest 'scalawags cops' should also be covered by a formal order," Lorenzana said.

Since Duterte took office in June last year, nearly 8,000 people, allegedly involved in drugs, have been killed in the campaign.