BEIJING — The Chinese police forcibly seized the ashes of a prominent Tibetan monk whose death in prison this month set off public demonstrations and raised suspicions about his treatment while incarcerated, supporters of the monk said on Tuesday.

Geshe Nyima, a cousin of the revered religious figure and community leader, Tenzin Delek Rinpoche, 65, said that four Tibetans transporting his cremated remains to his hometown, in the southwestern province of Sichuan, for Buddhist funeral rites were held at gunpoint by Chinese police officers last Thursday night in the town of Luding and forced to hand them over.

“The ashes were taken back and not given to the family,” said Geshe Nyima, speaking in a conference call from Dharamsala, India, where he lives in exile.

“Police said that they would throw the ashes into the nearby river. The four people don’t know what happened to the ashes.”