Iran's Supreme Court sentenced the first instance of "beheading" to three teenagers who committed theft under strict Islamic criminal law in this country.

Iran's Supreme Court this week upheld the sentence imposed at first instance trial against three minors, Hadi Rostami, Mehdi Sharafian and Mehdi Shahivand, who were convicted in November last year on four counts of theft in the city.

With the Supreme Court ruling, the three defendants will have to execute a four-finger decapitation on the right hand, under Iran's Islamic Criminal Law.

A June report by Iran's Human Rights Watch (IRM) said that Rostami, one of the four convicts, was in serious health while being held in Iran's central prison.

"According to article 278 of the Islamic Sanctions Act, four fingers on their right hand will be cut off for theft of property," the IRM said.

It is not clear when a penalty will be enforced and authorities have not provided more details on the charges of the defendants.

Finger cutting penalties based on draconian Islamic Sharia law in Iran are rarely used, and it is not clear how many Iranians are convicted under the law each year.

Amnesty International calls the sentence "a form of brutal torture".