MANILA - President Rodrigo Duterte's brutal drug war is an utter failure three years on, despite a state-sanctioned terror campaign that has led to thousands of extrajudicial killings, Vice-President Leni Robredo said on Monday (Jan 6).

"It's crystal clear... that despite the thousands who were killed, and despite the huge sum and resources spent, not even 1 per cent of the total supply of shabu and the money generated from illegal drugs were seized," Ms Robredo, who briefly took over Mr Duterte's crackdown on the drug trade, said at a news briefing.

"If this were an exam," she said, "the government's score would be 1 out of 100."

Her criticism drew a swift response from Mr Duterte's spokesman.

"It's a dud. She didn't say anything new... What was a failure was her stint (as drugs czar)," Mr Salvador Panelo told reporters. "I think she just wants to be relevant."

Citing official records, Ms Robredo said drug enforcement agents seized on average 1,000kg of shabu, or crystal methamphetamine, out of over 156,000kg circulating across the country each year.

An anti-money laundering body, meanwhile, froze just 1.4 billion pesos (S$37 million) out of an estimated 1.3 trillion pesos worth of drug money in circulation in 2016 and 2017.

Ms Robredo told reporters on Monday she gathered the information when she led the multi-agency body tasked to oversee Mr Duterte's controversial drug war.

In dismissing these numbers, Mr Panelo said he would let the government's drug enforcement agencies dispute Ms Robredo's report.

Mr Duterte had dared Ms Robredo to prove she could do a better job after she said in an interview that his drug war was "not working". Too many people had been killed in the crackdown, and still the problem persisted, she said.

Mr Duterte installed her as co-chair of the Inter-Agency Committee on Anti-Illegal Drugs on Nov 5 last year, but fired her just 18 days later.

During her brief stint, Ms Robredo met drug enforcement agents from the United States and the United Nations to ask them how they thought the anti-drug campaign could be refined and made less "anti-poor".

Later, she asked for a list of high-value targets in the drug war, after naming China as a major source of narcotics.

All this apparently did not sit well with Mr Duterte.

In short order, he called her a "scatterbrain", and warned her that she was "treading on dangerous ground" if she insisted on discussing the anti-drug campaign with "outsiders".

He accused her of "overreaching" and of "grandstanding" to push her presidential ambition, and said flatly that he could not trust her because she heads the opposition. The president and vice-president are elected separately in the Philippines.

On Monday, Ms Robredo said Mr Duterte's drug war was failing because it was not targeting big-time drug suppliers.

It was instead aimed at sowing fear in the country's poorest communities via drug raids that often led to suspects getting killed for purportedly fighting back.

Close to 6,000 mostly petty drug dealers and users have been killed in Mr Duterte's drug war after allegedly resisting arrest.

Human rights groups have cited a higher death toll and accused some policemen of killing unarmed suspects based on flimsy evidence and altering crime scenes to make it look like the suspects fought back violently.

"(The drug war) failed because they focused on street-level enforcement... Even if they go on drug raids every day, if they are not constricting supply, going after big suppliers, the problem won't end," Ms Robredo said.

But Mr Panelo contended that while Mr Duterte had yet to deliver on his promise to lick the drug menace, "there are already many drug-free districts (and) we have dismantled many drug factories".

"How can you say it's a failure?"