The government described the allegations as lies.

On Monday pro-Duterte senators who control the legislative chamber charged that de Lima’s investigation was ruining the country’s image.

The motion to oust de Lima — which was put forward by senator and boxer Manny Pacquiao - came after another senator, Alan Peter Cayetano, accused her of bias against Duterte.

“Senator de Lima, in her desire to destroy the president, is destroying the integrity and reputation of the senate,” Cayetano said in a speech.

De Lima walked out of the session hall during Cayetano’s speech because she could “no longer stand it,” she said. “I would now want to call it the tyranny of the majority. Now whether or not what’s done to me is fair or just, just let the people decide that.”

De Lima remains a member of the committee. Senator Richard Gordon, who has said Duterte should have the authority to suspend the writ of habeas corpus, will be the new chairman.

De Lima blamed Duterte for her ousting: “I know I will continue to be crucified because the president himself wants that... ever since I initiated the inquiry into his extra-judicial killings.”

“I don’t know what will happen now, whether this inquiry into the extra-judicial killings will at all be credible,” she said, warning the other senators would try to conceal the president’s culpability.

Human rights advocates said the move could derail accountability in the crackdown.

De Lima’s ouster “is a blatant and craven move to derail accountability for the appalling death toll from President Rodrigo Duterte’s abusive ‘war on drugs,’” US-based Human Rights Watch said.

“The Senate is showing greater interest in covering up allegations of state-sanctioned murder than in exposing them.”

The group called on senators opposed to Duterte’s tough tactics to seek de Lima’s reinstatement.

He won May elections by a landslide, after vowing to kill 100,000 criminals and rid the country of illegal drugs in six months.

“I did not realise how severe and how serious the drug menace was in this republic until I became president,” Duterte, 71, told reporters late Sunday in Davao.

“Even if I wanted to I cannot kill them all,” Duterte said, adding a new police list of drug suspects would be unveiled.

Maria Aurora Moynihan, 45, was shot by unknown attackers who left her by the side of a Manila street on September 10.

Her killers left a cardboard sign accusing Moynihan of being a “drug pusher for celebrities”, Chief Inspector Tito Jay Cuden said.

The victim was on bail while facing charges of possession of illegal drugs following a February 2013 suburban Manila police raid.

In a speech in Davao late Monday, Duterte brushed off any possible investigations into his crime war, which has attracted strong international criticism.

“Whether there will be a thousand investigations or (UN chief) Ban Ki-moon comes here, I don’t give a s***,” he said.

“I don’t care whether there is a thousand hearings everywhere... I will not stop until the last pushers on the streets are fully exterminated.”

Roman Catholic church bishops warned Monday that giving Duterte an extension would result in more summary killings.

“In the campaign, he categorically said that the drug problem would be solved in six months or he will step down, But of course he is not a man of (his) word,” Manila bishop Broderick Pabillo was quoted as saying on the bishops’s website.

Additional reporting by Associated Press