Leni Robredo, a critic of and rival to Philippine President Rodrigo Duterte, has accepted a job overseeing the government's controversial anti-drug campaign.

Duterte offered the post to Robredo, who is vice president, after her repeated criticism of his war on drugs.

What does Robredo want to do?

The appointment, which critics have suggested is an effort to tarnish an adversary, will put Robredo at the head of the crackdown.

"I want to fix the campaign against illegal drugs, stop the killing of innocents and bring to account abusive officials," Robredo told a press conference on Wednesday.

"If the president is thinking that I will keep quiet because I accepted the offer, he is wrong."

She will be the co-chair of a committee responsible for overseeing the crackdown, which was previously led by the national anti-drugs agency.

Duterte critics were skeptical of the appointment, with Senator Lila de Lima calling it a "silly trap." The president wants to "create the narrative of putting all the blame of his failures on someone else," added De Lima, who is imprisoned on drug charges she says are politically motivated.

What is the war on drugs?

Drug agents say they have killed just over 5,500 alleged dealers and users who fought back during arrest since the campaign began in 2016, according to AFP, but several watchdogs say the true toll is at least four times higher.

Opinion polls say the drug war has the overwhelming backing of Filipinos, yet it has high-profile critics among opposition politicians, the powerful Catholic church and advocacy groups.

Foreign institutions have also stepped in to question the killing, including International Criminal Court prosecutors who have launched a preliminary probe.

Advocates allege the campaign is a war on the urban poor which has had the side effect of unleashing a rush of killings linked to everything from personal disputes to political rivalries.

What has Duterte said?

Duterte's spokesman, Salvador Panelo, denied the appointment was an effort to drag Robredo into the campaign in order to co-opt her.

"Effectively, we're giving her a ladder to the presidency. This is her chance," Panelo said on Tuesday.

Duterte has previously derided Robredo's capability to potentially lead the country, which she would have to do if the president dies or cannot function.

But he said in a speech last week that the drug situation has "worsened" with the police on the "brink of surrendering."

"It's beyond my competence, but maybe she will do better," Duterte told reporters.