Amnesty International says Iranian officials have lashed and secretly executed two 17-year-old cousins in southern Iran.

The rights watchdog said Mehdi Sohrabifar and Amin Sedaghat were executed on April 25 at the Adelabad prison in Shiraz, the capital of the southern Fars Province. The two were arrested at age 15 and convicted on multiple rape charges after what international rights groups said was an unfair trial.

"The Iranian authorities have once again proved that they are sickeningly prepared to put children to death, in flagrant disregard of international law," said Philip Luther, Amnesty International's Middle East and North Africa director, in a statement on April 29.

"It seems they cruelly kept these two boys in the dark about their death sentences for two years, flogged them in the final moments of their lives, and then carried out their executions in secret."

The two were held in a juvenile prison facility since 2017 and on April 24 were transferred to Adelabad prison, where they were allowed to meet with their families.

The following day the relatives of the two boys were told by officials they had been executed and could claim their bodies.

Sohrabifar and Sedaghat claimed they had been beaten at a police detention center after they were arrested. During that time they also had no access to an attorney.

The rights group has recorded 97 executions of people under the age of 18 in Iran between 1990 and 2018.

Luther said Amnesty has seen a trend "in which Iran's authorities are carrying out executions of juvenile offenders in secret and without giving advance notice to the families, seemingly in a deliberate attempt to avoid global outrage."