Hong Kong police beat pro-democracy protesters in custody and committed acts that amount to "torture" during recent demonstrations, Amnesty International says in a new report that could fuel further unrest.

Police used "unnecessary and excessive force" in making arrests, beat a protester for declining to answer a question and then pinned him to the floor, shined laser pens in the eyes of people who had been detained and threatened to electrocute a man's genitals after he refused to unlock his phone, the human rights group said Friday.

Amnesty said its investigation included interviews with 21 arrested protesters, corroborating interviews with health care workers who treated demonstrators, and lawyers representing people who had been detained. Out of 21 protesters interviewed, 18 were hospitalized for injuries or illnesses related to their arrest and detention, the group said, adding that it also reviewed medical records.