Police in the Philippines are suspending their war on drugs until they have "cleansed" their ranks of "rogue" officers, the head of the national police force has said.

Ronald dela Rosa, the director-general of the National Police, told reporters on Monday that he was disbanding anti-drugs units following a botched kidnap-for-ransom operation of a South Korean businessman.

Jee Ick-joo's body was found inside the grounds of the national police headquarters in October. His head was wrapped in packaging tape and he had been strangled.

"To all the rogue cops, beware! We no longer have a war on drugs," Dela Rosa said.

"We will cleanse our ranks ... then maybe after that, we can resume our war on drugs. The president told us to clean the organisation first.

"I don't know how long it will take to cleanse the PNP. But with each and every one of us cooperating, helping each other, maybe in a month, we can do it," he added.

The campaign, which also includes officers going from house to house in search of drug suspects, has claimed the lives of more than 6,000 people, according to a police report cited by the Manila-based news website Rappler.

READ MORE: No peace for the dead in Rodrigo Duterte's drug war

Al Jazeera's Jamela Alindogan, reporting from the capital Manila, said the government and police force were sending conflicting messages.

On Sunday, President Rodrigo Duterte, who swept to power in May elections on a pledge to eradicate drugs, vowed to forge ahead with his war on drugs until the last day of his term.

"This is a complete turnaround from his election promise that he will be able to eliminate the presence of narcotics in his first six months of office," our correspondent said.

Senator Leila De Lima, Duterte's most outspoken critic, said the president and his police chief "should categorically give the order to end the killings".

The dismantling of the anti-drug units meant "they are aware that the very men involved in anti-drug operations ... are involved in illegal activities under the guise of the so-called war on drugs," she told ANC television.

Duterte's anti-drug campaign has caused alarm in the West, and rights groups accuse Duterte of turning a blind eye to a wave of alleged extrajudicial killings by police, mostly of low-level peddlers. Police deny this, claiming self-defence.