Indonesian police have arrested three former members of a minority religious sect on charges of blasphemy and treason.

They were from a group called the Light of Nusantara Movement, or Gerakan Fajar Nusantara (Gafatar), which was thrust into the limelight early this year after dozens of people who had been reported missing by their families were discovered to have left their homes to join it.

The sect was disbanded last August and declared as "heretical" in February by the country's top Islamic body, Indonesian Ulema Council. Clerics said the group deviated from mainstream Islam as it attempted to combine Islamic, Christian and Jewish beliefs.

Brigadier-General Agus Andrianto, the national police's general crimes director, told reporters yesterday that the sect's spiritual leader Ahmad Musaddeq and followers Mahful Muis Tumanurung and Andri Cahya were arrested on charges of blasphemy. The latter two are also suspected of treason over a plan to build a new state.

The police have confiscated brochures about the sect and its organisational structure, as well as documents and holy books that have "fused" the Quran, the Bible and Jewish doctrine, the brigadier-general added.

Ahmad, who had previously declared himself as the group's "prophet", was jailed for four years in 2008 for blasphemy. He re-established the group in January 2012 after his release.

A series of alleged abductions led police to the group's remote village in Mempawah district in West Kalimantan in January.

Hundreds of followers have since been taken back to their home towns by the central government after a local mob burned down their village, displacing some 1,500 people.

They were evacuated by the authorities first to temporary shelters and then to Indonesia's main island of Java, some by warship.

Human Rights Watch estimated the group to number more than 7,000 as of March.

Rights groups have condemned the latest arrests as "ridiculous".

"One's faith cannot be criminalised. They are such a tiny group and have no weapons, so it's just impossible that they are trying to create a new state," Setara Institute researcher Ismail Hasani told The Straits Times.

Indonesia officially recognises six religions - Islam, Catholicism, Protestantism, Confucianism, Buddhism and Hinduism.

The world's most populous Muslim nation is largely viewed as tolerant, but has seen a spike in violence against religious minorities in recent years.

National police spokesman Boy Rafli Amar told reporters: "We don't want this Gafatar movement to clash with existing religions in the country and stir anxiety in the community. It creates confusion."