MANILA - An international human rights group on Sunday urged the Philippine government to scrap the "politically motivated" drug charges against Senator Leila de Lima.

The Human Rights Watch (HRW) said the Duterte administration is abusing the judicial system to punish critics of its war on drugs, as in the case of De Lima, who once initiated a Senate inquiry into the President's brutal anti-narcotics campaign.

"The prosecution of Senator Leila de Lima is an act of political vindictiveness that debases the rule of law in the Philippines,” said Phelim Kine, HRW deputy Asia director.

“The Duterte administration seems intent on using the courts to punish prominent critics of its murderous war on drugs,” he continued.

The justice department on Friday filed non-bailable drug trafficking cases against De Lima, based on the testimonies of several high-profile inmates who accused her of accepting drug payoffs when she was still justice secretary.

HRW said the the case is part of a "relentless government campaign of harassment and intimidation" allegedly in response to De Lima's criticism of the anti-drug crackdown.

Duterte, the group noted, first assailed De Lima's character by claiming the senator was having an affair with her married driver, after she initiated a Senate inquiry on the drug war.

The President's attacks on De Lima intensified after her witness, self-professed hitman Edgar Matobato accused the President of ordering assassinations when he was still Davao mayor, HRW claimed.

The group noted that "pro-Duterte" senators later tagged De Lima as "biased" against the president and ousted her as the chair of the Senate justice committee.

“The politically motivated case against De Lima shows how Duterte‘s ‘war on drugs’ threatens not only the thousands of people targeted, but the criminal justice and political systems,” Kine said.

“It’s more important than ever that concerned lawmakers and foreign governments step up to denounce the Duterte administration’s disregard for basic human rights.”

Justice Secretary Vitaliano Aguirre earlier insisted that the cases against De Lima were not politically-motivated.

A judge will decide whether to issue a warrant for her arrest once her case is assigned to a court.

If convicted, De Lima faces between 12 years to life in prison. Under the law, legislators only enjoy privilege from arrest for crimes punishable by fewer than 6 years’ imprisonment.