Manila (Reuters): The Philippines police came under pressure on Friday to explain the killing of a high-school student after the 17-year-old became one of at least 80 people shot dead this week in an escalation of President Rodrigo Duterte's ruthless war on drugs .

Television channels aired CCTV footage that showed Kian Loyd Delos Santos being carried by two men to the place where his body was later found, raising doubt about an official report that said he was shot because he fired at police officers first.

Witnesses told the ABS-CBN channel that the teenager did not have a firearm and police officers at the scene handed him a gun, asked him to fire the weapon and run.

National police chief Ronald dela Rosa said that if the Grade 11 student did not pose a threat, the officers who shot him on Thursday night would be held accountable.

"Just think about it, he is just a kid. If that happened to your sibling?" he said on GMA TV. "We will investigate it, I assure you."

Metro Manila police chief Oscar Albayalde said the three policemen involved had been relieved of their duties and an investigation would be launched into the incident, which took place in the Caloocan district in the northwest of the capital.

Police killed at least 13 people in Manila on the third night of a new push in Duterte's war on drugs and crime, taking the toll for one of the bloodiest weeks so far to 80, Reuters witnesses and media reported.

Earlier this week, 67 people were gunned down and more than 200 arrested in Manila and provinces adjoining the Philippines capital, in what police described as a "One-Time, Big-Time" push to curb drugs and street crimes.

The term has been used by police to describe a coordinated drive in crime-prone districts, usually slums or low-income neighborhoods, often with additional officers.

The spike in killings drew condemnation from Vice President Leni Robredo, who belongs to a party opposed to Duterte.

Branding it "something to be outraged about", she has been a constant critic of the crackdown that has killed thousands of Filipinos and caused international alarm since Duterte took office over a year ago.