Sentencing rapists to death, as Bangladesh did Thursday, is not an appropriate punishment even for such a heinous crime, the UN rights chief said.
"Tempting as it may be to impose draconian punishments on those who carry out such monstrous acts, we must not allow ourselves to commit further violations," Michelle Bachelet said in a statement.
Her comment came after a Bangladesh court sentenced five men to death Thursday for the 2012 gang-rape of a 15-year-old girl.
It marked the first conviction since the government of Prime Minister Sheikh Hasina this week introduced the death penalty for rape.
Gang-rape already carried the death sentence, but rape by a single offender had previously been punishable only by life imprisonment.
Bachelet cited the law change in Bangladesh, but also calls in a number of other countries to impose the death penalty for rape.
She highlighted calls in Pakistan for public hanging and castration of rapists, and a law introduced in the northwestern Nigerian state of Kaduna last month imposing surgical castration followed by execution in rape cases where the victim is under 14.
"The main argument being made for the death penalty is for it to deter rape – but in fact there is no evidence that the death penalty deters crime more than other forms of punishment," Bachelet said.
"Evidence shows that the certainty of punishment, rather than its severity, deters crime."
She stressed that in most countries, "the key problem is that victims of sexual violence do not have access to justice in the first place."
This was due to a range of factors, including "stigma, fear of reprisals, entrenched gender stereotypes and power imbalances," she said, stressing that handing the death penalty to perpetrators would not remove those barriers.