The reported sentencing to paralysis for a Saudi man for a crime he committed as a 14-year-old has been condemned as "grotesque" by the Foreign Office.

The punishment, which was reportedly handed down to 24-year-old Ali al-Khawahir for stabbing his friend in the back 10 years ago, should not be carried out, the FCO said.

Khawahir will be paralysed from the waist down unless he pays 1m Saudi riyals (£177,000) in compensation to the victim, according to Amnesty International, who quoted reports in Saudi Arabian media.

An FCO spokesman said: "We are deeply concerned by reports that a Saudi Arabian court has sentenced a man to be paralysed in retribution for causing the paralysis of a friend when he was 14 years old.

"We urge the Saudi authorities to ensure that this grotesque punishment is not carried out. Such practices are prohibited under international law and have no place in any society."

Amnesty condemned the punishment as "utterly shocking".

A similar sentence of paralysis imposed in Saudi Arabia in 2010 is not known to have been carried out, the charity said.

If implemented, the paralysis sentence would contravene the UN convention against torture and the principles of medical ethics adopted by the UN general assembly, Amnesty said.

Ann Harrison, the charity's Middle East and north Africa deputy director, said: "Paralysing someone as punishment for a crime would be torture. That such a punishment might be implemented is utterly shocking, even in a context where flogging is frequently imposed as a punishment for some offences, as happens in Saudi Arabia.

"It is time the authorities in Saudi Arabia start respecting their international legal obligations and remove these terrible punishments from the law."

Saudi courts regularly sentence people to forms of corporal punishment, according to the charity. In retribution cases, sentences have included eye-gouging, tooth extraction and death.

In such cases, the victim can demand the punishment be carried out, request financial compensation or grant a conditional or unconditional pardon.

Flogging is mandatory for a number of offences and can also be imposed at the discretion of judges as an alternative, or in addition to other punishments, Amnesty said.

Thieves are often sentenced to amputation of the right hand, while "highway robbery" is punished by cross amputation – cutting off the right hand and the left foot.