Investigators with Israel's prison service on Thursday concluded arson led to 9 prisoners being injured in a cell-block fire at Massiyahu prison earlier in the day.
Prisoners in Cell Block 14 set a mattress on fire to protest their incarceration, the investigators said.
One prisoner was reported as being in a critical condition and two others were in a serious condition after detainees set fire to a mattress in the prison, located near Ramla.
The others were described as having been "lightly injured."
All 9 injured prisoners were taken to Assaf Harofeh Medical Center in Tzerifin, Sheba Medical Center in Tel Hashomer and Kaplan Medical Center in Rehovot.
Contrary to claims in Palestinian Authority affiliated news sources, who claim the injured prisoners were Arabs from PA enclaves, authorities did not specify the nationality, ethnicity, or classification of the prisoners involved in the incident.
However, Massiyahu prison is generally reserved for non-violent prisoners who do not pose a significant security risk, and illegal immigrants and others facing deportation.
Massiyahu prison is famous for having a religious wing, nicknamed "Beit Midrash Maasiyahu" (Massiyahu Study Hall) because of the wholesome religious environment and constant Torah study that occurs in that wing.
Former Israli politician Shlomo Benizri and former President Moshe Katsav, are incarcerated in "Beit Midrash Massiyahu."