MANILA (Reuters) - A staunch critic of Philippine leader Rodrigo Duterte on Tuesday urged the Cabinet to declare the president unfit to rule, describing him as a “sociopathic serial killer” because of his war on drugs and allegations he once ran a hit squad.

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Senator Leila de Lima, one of the few high-profile critics of Duterte’s crackdown, said Filipinos should rise up and Cabinet ministers had the duty to save the country from a president “of criminal thinking”.

De Lima is facing arrest on charges of involvement in the drugs trade, which she says are a vendetta for her leading a Senate investigation of allegations that Duterte had ordered unlawful killings of criminals while mayor of Davao City.

Duterte denied unlawful killings and the Senate investigation found no evidence to prove that.

She said new allegations made on Monday by a retired policeman, Arturo Lascanas, that Duterte had operated a “Davao death squad” should clear up any uncertainty.

Duterte’s lawyer and his spokesmen have rejected Lascanas’ claims.

“With the coming out of Lascanas, there’s no more doubt that our president is a murderer and a sociopathic serial killer,” De Lima told reporters.

“I will not retreat from this fight now that I know I am not alone. We are plenty already, so they should be scared. I call on all our countrymen that have yet to act, to hold responsible the murderer president of the country.”

The war on drugs has broad public support despite the killing of more than 7,700 people since Duterte took office on June 30, about 2,500 in police operations.

The cause of other deaths are much in dispute, attributed by police to vigilantism, turf wars, or everyday murders unrelated to drugs. Activists are convinced many are extrajudicial killings, carried out by police or with their encouragement.

Asked at a regular news briefing about De Lima’s remarks, Duterte’s spokesman, Ernesto Abella, said: “That’s colourful language”.

De Lima and several associates were last week charged in drug-related cases, based on the testimony of convicts and former prison officials at last year’s congressional inquiry on the drug trade in jails.

She has yet to be arrested and has filed a motion to quash the charges on the grounds the court had no jurisdiction.