The IHRDC reported that the teenager, whose name it withheld for his safety, was held among bodies of slain protestors transferred to the Kahrizak Forensic Center south of Tehran where he stayed motionless until his family eventually found him alive.
It added it was not able to independently verify the account as a nationwide internet blackout persists in Iran.
The youth, who is under 18, was in critical condition after suffering gunshot wounds.
“During the three days he was held among the bodies transferred to Kahrizak, he heard the ringing of cell phones among the corpses and smelled the intense stench of decay,” the Iran Human Rights Documentation Center said, citing the teenager’s account.
The group said the young man described hearing gunfire after sounds from wounded detainees, suggesting they were summarily executed.
“The witness reported that whenever groans from the wounded were heard, they were shortly followed by the sound of gunfire and the cessation of the groaning, strongly indicating that security forces delivered fatal shots to wounded individuals who were still alive,” IHRDC said.
“These details raise serious concerns regarding the treatment of the wounded, violations of the right to life, and extrajudicial killings, including of minors, during the suppression of protests,” the rights group added.