Indonesian authorities raided a university dormitory in Surabaya on Saturday and arrested dozens of West Papuan students after a standoff over allegations the Indonesian flag was thrown into a sewer.

Officers broke down the gates of the Surabaya building and used teargas to clear the rooms, taking 43 people into custody on the Indonesian Independence Day weekend.

Surabaya police told Kompas news the students were brought in for questioning over the “destruction and disposal” of the Indonesian flag, which had been hanging outside the student hostel.

The students were released around midnight after questioning.

Surabaya city police chief, Senior Commissioner Sandi Nugroho, told the Jubi news outlet that witnesses claimed the individual who damaged the flag had gone inside the student accommodation.

Reports of the damaged flag had reportedly spread on social media, drawing a crowd of residents to the building to protest on Friday and Saturday, allegedly shouting anti-West Papuan slogans and threats, and singing the Indonesian national anthem.

16/8/19 Surabaya, Java



Ini yel-yel massa sepanjang malam: “usir, usir Papua! Usir Papua sekarang juga!”



Mob rounding up West Papuan students’ dorm were singing this all night “kick out, kick out Papua! Kick out Papua right now!”



They are still trapped inside. pic.twitter.com/HGKQkmE6CJ — Veronica Koman (@VeronicaKoman) August 17, 2019

On Friday night police urged the crowds outside the student accommodation to leave.

On Saturday afternoon police fired teargas into the building. CNN Indonesia reported at least 23 shots of teargas were fired.

The Indonesian human rights lawyer Veronica Koman accused the police of a “totally disproportionate” response, and alleged a number of students were injured during the raid.

“Fully armed police shot teargas into the dorm, charged into it, forced the students to squat and waddle along the ground, then arrested them,” Koman said.

“They were released at almost midnight. The students still could not go in because the teargas still smelt strong. Some of their stuff are still confiscated without any warrant.

“The arrest is totally disproportionate. The students were not even told why they were arrested. That violates the criminal procedural law.”

Guardian Australia has attempted to contact the East Java Regional Police for comment.

Koman said two Indonesian students who had attempted to bring food and water to the students on Saturday, prior to the raid, were beaten and arrested.

She said she had been speaking to the students on Friday night and could hear “racists chants” through the phone.

“People demanded the students to come out so they can kick them out from the city and kill them,” she said.

“They chanted ‘Out! Out! Papua out!’, ‘massacre Papua! massacre Papua’. The crowd sang Indonesian anthem until past midnight.”

CNN Indonesia also reported the chants from the crowd, which it said included people wearing clothing referencing the Islamic Defenders Front (FPI) and the far-right Pancasila Youth organisation.

West Papua has been locked in a civil conflict for decades over its demands for independence from Indonesia, which annexed the territory on the western half of the island of Papua in the 1960s. In that time there have been claims of up to half a million people killed, and Indonesia has been accused of human rights violations, including arbitrary arrests and extrajudicial killings.

Reports of growing support among non-Papuan Indonesians have bolstered the independence movement, and Koman said harassment and intimidation of West Papuans in Indonesia was worsening.

“Last year, mobs forced to fly Indonesian flag at the same location,” she said.

“This only happens towards the West Papuans.”

Last week Indonesian authorities broke up a number of protests across Indonesia – timed to coincide with consideration of the West Papuan independence claim at the Pacific Islands Forum – with mass arrests and some violence.