Manila - The Philippines faced calls Friday to investigate its firebrand president after a self-confessed hitman alleged Rodrigo Duterte ordered a thousand opponents and suspected criminals murdered when he was a city mayor.
The hitman told a Senate inquiry on Thursday that he and a group of policemen killed some 1,000 people in Davao city on Duterte's orders from 1988-2013, with the politician himself shooting dead one of the victims.
"These are serious allegations and we take them seriously, we look into them," said US State Department deputy spokesperson Mark Toner.
Critics say the alleged killings in Davao, where Duterte was mayor for more than 20 years, established a pattern that has spread nationwide under the new presidency.
The allegations surfaced as the Senate investigated alleged extra-judicial killings in an ongoing anti-drug crackdown that has led to more than 3,000 deaths in Duterte's first 72 days in office.
US-based watchdog Human Rights Watch urged Manila to let United Nations investigators probe the claims.
"President Duterte can't be expected to investigate himself, so it is crucial that the United Nations is called in to lead such an effort," the monitor's Asia director Brad Adams said in a statement.
Duterte had on various occasions admitted or denied involvement in the death squads during the campaign for May elections, which he won by landslide on a pledge to kill tens of thousands of criminals.
Duterte has so far ignored the latest allegations while his senior aides dismissed them, with Justice Secretary Vitaliano Aguirre branding them "lies and fabrications".
Wilnor Papa, a campaign officer for the Manila office of Amnesty International, said the problem of impunity was coming to a head partly due to the failure of previous governments, which failed to prosecute Duterte.
"We are now seeing riding-in-tandem (motorcycle-borne assassins) like those that prowled the Davao streets in the late 1990s, The targets are not only drug syndicates. Even purse snatchers use them and they can target basically anyone," he told AFP.
House of Representatives member Edcel Lagman urged Duterte Friday to name an independent fact-finding commission made up of retired judges to "determine the identities of the principals and perpetrators as well as of the victims".
The fate of the former death squad member, Edgar Matobato, was uncertain on Friday as the Senate president, Duterte ally Aquilino Pimentel, refused to take him into protective custody.
His testimony was not related to the drug war killings being investigated, Pimentel told AFP, adding: "There's even no showing that his life or safety is threatened."