Philippine police have arrested a doctor in the capital Manila, accusing her of being a leader of a Maoist rebel group that has waged a decades-long insurgency against the government.

Maria Natividad Castro, 53, is being held without bail and will be tried on charges of kidnapping, for which a lower court had ordered her arrest in 2020, according to a police statement issued on the night of February 18.

But her former employer, human rights monitor Karapatan, said Castro is facing “trumped up” charges after she investigated alleged human rights violations in the volatile Mindanao region while also setting up community health centres there.

She was arrested at her home on February 18 and accused of being part of the Communist Party of the Philippines’ central committee.

“Karapatan denounces the arrest of human rights and health worker, Dr Naty Castro, as yet another form of attack against human rights defenders,” the group said, referring to Castro by her nickname.

Critics say allegations of communism – known locally as “red-tagging” – have been used to discredit and detain activists, journalists, lawyers and dissidents.

While the practice is not new in the Philippines, it has intensified under President Rodrigo Duterte, according to rights groups.

At the start of his term in 2016, Duterte, a self-described socialist, had sought a peace deal with the rebels.

But after talks collapsed in 2017, he branded the Communist Party and its armed wing “terrorist organisations” and ordered soldiers to shoot female insurgents in the genitals.

On Facebook, Castro’s brother insisted she was just a health worker who had served indigenous communities.

“My sister is accused of multiple charges of kidnapping and illegal detention, all related to her human rights advocacy. ALL UNTRUE,” he wrote.

Philippine police chief Dionardo Carlos congratulated the force on Castro’s arrest, saying in the statement they made “it possible to bring the suspect before the court”.