Andrie Yunus, deputy coordinator of KontraS, 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 has detained four soldiers from the armed forces' intelligence unit suspected of involvement in the assault, commander Yusri Nuryanto said.

An internal investigation into the attack had found "irregularities" that led to the detentions, Yusri said, without giving further details.

"We are still investigating the motives of the four alleged perpetrators," he 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 added.

Separately, Jakarta police released CCTV footage 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.

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

Lawmakers agreed on Wednesday to form a special committee to oversee the handling of the case, according to member of parliament Habiburokhman, who like many Indonesians uses only one name.

Andrie has been a vocal critic of moves to increase the influence of the military in the Indonesian government and had recently recorded a podcast on the issue when he was attacked.

UN rights chief Volker Turk said last week 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.