The torching of a Shia-run Islamic boarding school in East Java on Thursday stemmed from a sibling dispute after a cleric at the school denied his brother the right to enter into polygamous marriage with one of the students, a teacher said.

"A male resident sought revenge on his brother, a Shia cleric who refused to let him marry one of his female students as it would be polygamy," said Ustadz Muhyi, one of the teachers at Tajuk Muluk Islamic boarding school (pesantren) in Sampang district.

The pesantren was destroyed in Thursday's blaze, but there were no reports of injuries. The pesantren houses about 100 male and female students.

According to Ustadz, the cleric's brother and community leaders stoked anti-Shia sentiments among nearby residents. The Shia, like the Ahmadiyah, are facing growing persecution and discrimination from local people in Indonesia. The rising intolerance against minority groups in the country has received international condemnation, including from Human Rights Watch.

Ustadz said a crowd of roughly 1,000 people showed up at the school on Thursday morning and watched as the pesantren's buildings, including a mosque, were set on fire. "There was no security there when the mob arrived and burned the school," he said.

National Police spokesman Insp. Gen. Saud Usman Nasution denied allegations that police had let the attacks occur. "The police have tried to visit the location. But we were intercepted by a mob," Saud said.

Moh. Hadun Hadear, a member of Islamic organization Ahlul Bait Indonesia, said that prior to the burning of the school, there had been rumors that an attack was being planned and despite appeals to the police for help, nothing had been done.

In September, prominent Human Rights Watch activist Andreas Harsono and an Australian researcher were taken into custody by police in Sampang as they attempted to investigate the local Shia population. The pair were taken to Sampang Police headquarters and interrogated for nine hours but were released due to a lack of charges.