Philippine President Rodrigo Duterte fired vice-president and arch-critic Leni Robredo from her post as overseer of his drug war on Sunday, an aide said, just days after calling her a "scatterbrain" not to be trusted with state secrets.

Why was Robredo fired?

Robredo, 54, lasted less than three weeks steering Duterte's signature anti-narcotics campaign, which she vowed to reform amid allegations of police abuses.

Duterte took issue with Robredo's meeting U.S. embassy and United Nations drug experts. "I do not trust her," Duterte told reporters on Tuesday, calling her a "scatterbrain" who could inadvertently share sensitive security matters with outsiders.

"The vice-president resorted to unduly baiting international attention on the matter," Duterte spokesman Salvador Panelo said in a statement announcing Robredo's immediate dismissal.

"Essentially, what the vice-president has done is to embarrass our country," Panelo added.

Robredo's spokesman said he was not aware of her receiving any formal dismissal notice, adding "as usual, announced to media without the courtesy of directly informing (her).”

The decision came after Duterte and his political allies publicly criticized Robredo, who had vowed to end "senseless" killing in the campaign after her appointment.

Why was she appointed?

Critics were skeptical of the appointment from the start, questioning whether it was a trap to tarnish Robredo or simply an impulsive response to her repeated criticism of the drug war.

Robredo, who was elected separately from the president, surprisingly accepted on November 6 Duterte's offer of the post despite warnings from allies.

"From the start Robredo was set up to fail," said opposition lawmaker Edcel Lagman. "The president cannot allow her to succeed... where he himself has failed."

Duterte had previously derided the capability of Robredo to lead the country, which she would have to do if the president dies or cannot function.

What's the background?

The drug war is overwhelmingly backed by Filipinos, but critics allege it is a war on the urban poor with the side effect of unleashing a rush of killings linked to everything from personal disputes to political rivalries.

Police say they have killed just over 5,500 alleged dealers and users who fought back during arrest, but watchdogs say the true toll is at least four times higher.

International Criminal Court prosecutors have launched a preliminary probe of the killing, and the UN's top rights body voted in favor an in-depth review.

(With input from AFP)