A Philippine senator and leading critic of President Rodrigo Duterte's deadly anti-drug crackdown has been arrested on drug charges after it was alleged she received money from drug dealers inside the country's prisons.

Key points: Lima says the charges are a vendetta for investigating Duterte

Lima says the charges are a vendetta for investigating Duterte Officials say Lima should welcome the arrest to prove her innocence

Officials say Lima should welcome the arrest to prove her innocence Lima says it is "an honour" to be jailed for fighting Duterte

Senator Leila de Lima, her former driver and bodyguard and a former national prison official were ordered to be arrested by a local court after a judge found merit in criminal charges filed by the Department of Justice last week.

"The truth will come out and I will achieve justice. I am innocent," she told reporters shortly before being escorted away.

"If they think they can silence me, if they think I will no longer fight for my advocacies, especially on the truth on the daily killings and other intimidations of this Duterte regime, it's my honour to be jailed for what I've been fighting for."

Ms Lima, a human rights lawyer before joining government, said the charges were a vendetta against her after she last year led a Senate probe into alleged extrajudicial killings during Mr Duterte's anti-drugs crackdown.

A police convoy, trailed by media vans, took Ms Lima to the main police camp, where officers took her photograph and fingerprints before her detention.

On Tuesday, Ms Lima described Mr Duterte as a "sociopathic serial killer" and urged his cabinet to declare him unfit to rule because he had a "criminal mind".

Presidential spokesman Ernesto Abella called Ms Lima's arrest "a major step forward in the administration's anti-drug war".

Arrest could be 'wakeup call' Philippines needs: Lima

According to complaint filed at a regional trial court, Ms Lima received 5 million Philippine pesos ($130,000) delivered by the former prison official to her home when she was justice minister between 2010 and 2016 — the criminal cases filed against the senator and two others are non-bailable.

"These are all lies," Ms Lima said, adding that the case against her arrest might be the "wakeup call" the country needs, referring to the absence of a public outcry in the country over the killings in the anti-drug campaign.

Mr Duterte's chief legal counsel, Salvador Panelo, said in a statement on Thursday that Ms Lima should "welcome this development as she is now given the opportunity to refute any and all allegations and/or evidence to be presented by the prosecution against her".

About 7,700 people have died in the drug crackdown, with more than 2,500 people killed in operations when street-level drug peddlers resist arrest and fight back, according to police.

In September last year, Ms Lima was removed by Mr Duterte's allies as head of the investigation into extrajudicial killings and just days later came under investigation herself in a congressional inquiry in which witnesses testified to her having pivotal role in the narcotics trade.

Reuters/AP