BEIJING—Three Tibetans have died after setting themselves on fire to protest Chinese rule in a western region where authorities have imposed a heavy security presence, exiled Buddhist monks and reports said Thursday.

More than 100 Tibetans have self-immolated since 2011 to protest Chinese policies in the region and call for the return of their beloved spiritual leader, the Dalai Lama, from exile.

Two of the three latest protesters were monks at a monastery in Ruo'ergai county of Aba prefecture, according to exiled monks and the Free Tibet group. The two monks, aged 20 and 23, set themselves on fire in a corner of an assembly hall of the Taktsang Lhamo Kirti monastery, wrote Losang Yeshe and Kanyag Tsering, monks living in exile in Dharmsala, India.

U.S. broadcaster Radio Free Asia reported that a Tibetan woman in Rangtang county in the same prefecture also died after self-immolating Wednesday. The broadcaster said the woman was 23 years old, but that other personal details were not known.

Police and propaganda officials in both counties were either unreachable by phone or said they were unaware of the self-immolations.