Andrie Yunus, deputy coordinator of the KontraS rights group, was riding a motorbike last week when he was approached by two men on a scooter, one of whom threw acid at him, according to the group.

He suffered injuries to his face, an eye, hands and torso.

The military police have detained four soldiers from the armed forces' intelligence unit suspected to have ties to the assault, commander Yusri Nuryanto said.

An internal investigation after the attack had found "some irregularities" that led to the detentions, Nusri said, without giving further details of their alleged crimes.

"We are still investigating the motives of the four alleged perpetrators," Yusri told a press conference.

The soldiers, identified by their initials NDP, SL, BHW and ES, will be held at a maximum security facility in Jakarta, he said.

Separately, Jakarta police released CCTV recordings on Wednesday showing the faces of two people suspected of attacking Andrie.

They had the initials BHC and MAK, police official Iman Imanuddin said. Their links to the four soldiers are unclear.

The police will corroborate their findings with the armed forces, Iman said when asked about the military detentions.

On Monday, police said analysis of CCTV footage showed four suspects on two scooters had followed Andrie before the attack.

Andrie has been a vocal critic of moves to increase the influence of the military in the Indonesian government and had just finished recording a podcast on the topic when he was attacked.

UN rights chief Volker Turk last week said he was "deeply concerned" by the "horrific" attack and called for accountability.

Human Rights Watch says Indonesia "has undergone further democratic backsliding, crackdowns on protests, media censorship, and intimidation of activists" under President Prabowo Subianto, an ex-general in office since 2024.