Anyone raping a child under age 14 will face the death penalty in state of Kaduna.
Men convicted of rape will face surgical castration under the new legislation.
UN Human Rights Commissioner Michelle Bachelet condemned the plans today.
She 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'.
The UN has condemned plans to castrate rapists and paedophiles in Nigeria and called the measures 'draconian'.
In September, the governor of Nigeria's Kaduna state signed a law saying men convicted of rape would be subjected to surgical castration - with those found guilty of raping a child under the age of 14 facing the death penalty.
The measures followed public anger over a recent increase of rapes amid Covid-19 restrictions, which prompted the nation's state governors to declare a state of emergency.
Today, the UN's High Commissioner for Human Rights Michelle Bachelet condemned the plans, calling them 'draconian'.
'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,' she said.
In a statement regarding the adoption of the law in Nigeria, Bachelet said the main argument made for instituting the death penalty is to deter rape. She added that the assumption that the punishment prevents sexual assaults is wrong.
She said 'the certainty of punishment, rather than its severity, deters crime'.
'Penalties like surgical castration and bilateral salpingectomy will not resolve any of the barriers to accessing justice, nor will it serve a preventive role,' Bachelet argued.
'Surgical castration and salpingectomy violate the absolute prohibition of torture and other cruel, inhuman or degrading treatment or punishment under international human rights law.'
Reported cases of rape in Nigeria have risen dramatically during the months of coronavirus restrictions.
Women's groups have called for tougher action against rapists, including the death penalty.
Kaduna state's new law is the strictest against rape in Nigeria, Africa's most populous country.
The state's newly amended penal code also says a person convicted of raping someone over age 14 will face life imprisonment.
The previous law carried a maximum penalty of 21 years' imprisonment for the rape of an adult and life imprisonment for the rape of a child.
A woman convicted of rape of a child under 14 faces the removal of her fallopian tubes.