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 Britain's 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 on Thursday.

Al-Khawahir will be paralysed from the waist down unless he pays one million Saudi royals ($257,900) 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.