MANILA - Authorities will "never back down" from investigations into the hundreds of killings that are being linked to President Rodrigo Duterte's war on illegal drugs, the chief of the Philippine National Police (PNP) said Friday.

The police leadership will face a Senate investigation next week, as international criticism mounted over alleged human rights abuses due to the President's relentless anti-crime campaign.

Director General Ronald "Bato" dela Rosa, the PNP chief, said the nearly two-month-old campaign has been marked with both high and low points.

"High pag maganda accomplishment natin. Pag low, pag tayo ay iniimbestigahan pero patuloy pa din, nakatayo pa din tayo and ready to face the elements of the environment [High, when we have good accomplishments. Low, when we are being investigated, but we stand strong and ready to face the elements of the environment]," he said.

"We can stand, and never back down," Dela Rosa said in a speech before rain-soaked policemen. "Tiisin nyo yang ulan ha kayang kaya yan [Don't mind the rain. You can do it]."

Dela Rosa faced the Senate Committee on Public Order and Dangerous Drugs Thursday, ahead of formal hearings on Monday, which will be spearheaded by Sen. Leila de Lima, a staunch critic of the President.

Data from ABS-CBN Investigative and Research Group showed that from May 10, when Duterte's election mandate became clear, until Thursday, 1,103 drug suspects have been killed, 666 of which in police operations. The fatalities also include 343 who were gunned down by unidentified assailants and 94 whose bodies were found away from the crime scene.

Dela Rosa told senators on Thursday that the PNP was investigating 899 deaths from July 1 to August 15.

"Ipagpatuloy lang natin ang kampanya, basta lahat ng ginagawa natin ay sa ilalim ng batas at paggalang sa karapatang pantao [Let us continue our campaign against illegal drugs, as long as everything we do is within the law, and with respect for human rights]," he told policemen Friday.