A group of men were detained in South Jakarta police station after police raided an alleged “gay sex party” at a private home. They were released Sunday night.

The 13 men were arrested after 50 members of a religious extremist mob Islamic Defenders Front (FPI) barged into an apartment in the Kalibata City apartment complex and forced the police to arrest participants in what they believed was a gay sex party.

The apartment was raided and condoms and phones were seized, with the mobiles allegedly showing a WhatsApp group used to organise the party.

It is not illegal for such events to be held.

“There's no arrest. The police just secured them, questioned and after finding out that there's no crime in it, we sent them home," Jakarta Police spokesman, Senior Commissioner Prabowo Argo Yuwono told AAP on Monday.

“We are not sure if there was any prostitution, all we know is they were playing some games there,” he told reporters.

FPI’s public relations division said on their Twitter account @HumasFPI on Sunday that the group’s “investigation unit” along with the police “successfully broken up” the alleged sex party.

Andreas Harsono from Human Rights Watch said the raid was yet "another setback for Indonesia's fledgling democracy.”’

“People's privacy is being trampled in the name of Islamic morality," he told AAP. "The police should not work with any vigilante groups in Indonesia. It is an old practice but it should stop.”