Despite calls by human rights group Amnesty International for an 11th-hour stay of the 17-year-old's execution, Alireza Molla-Soltani was sent to the gallows at the scene of the crime in the city of Karaj, west of the capital.

A large crowd of people had gathered to witness the hanging and security forces were present "to ensure the sentence was carried out without any glitches," the official IRNA news agency reported.

Molla-Soltani was sentenced to death last month for stabbing the popular athlete, Ruhollah Dadashi, to death in mid-July.

The teenager said at his trial he had killed only in self-defence after a driving dispute led him and two other youths into a confrontation with Dadashi, according to Amnesty.

A spokesman for the prosecution, Ali Ramezanmanesh said the boy had reached "religious maturity" and was over 18 years of age.

"The law views religious maturity as its criterion which is calculated according to the lunar calendar, therefore the convict is over 18 and there are no legal impediments" in the way of the hanging, he told Fars news agency.

The Islamic lunar calendar is some 11 days shorter than the solar calendar, with 354 days a year.

"Executing juvenile offenders is strictly forbidden under international treaties that Iran has signed up to," said London-based Amnesty's deputy director for the Middle East and North Africa, Hassiba Hadj Sahraoui.

Along with China, Saudi Arabia and the United States, Iran has one of the highest numbers of executions each year.

The latest hanging brings to 202 the number of executions reported in Iran so far this year, according to an AFP tally based on media and official reports.

Iranian media reported 179 hangings last year but international human rights groups say the actual number was much higher, ranking the Islamic republic second only to China in the number of people it executed in 2010.

Tehran says the death penalty is essential to maintain law and order, and that it is applied only after exhaustive judicial proceedings.

Murder, rape, armed robbery, drug trafficking and adultery are among the crimes punishable by death in Iran.