In a statement released on Monday, the London-based rights group said Musa Mahmudi and Ehsanullah Hamidi were detained by the National Directorate of Security (NDS) on Thursday as they were on their way to meet with the European Union ambassador in Kabul.
Mahmudi, a youth social worker, told local TV network TOLO News as well as The Guardian newspaper that teachers and local officials were involved in the paedophile ring, based in Logar province south of the capital.
At least 546 boys from six schools were allegedly abused, The Guardian reported. Authorities have not confirmed the allegations.
Some victims were later killed, The Guardian reported, adding that rights campaigners uncovered more than 100 videos of the sexual abuse.
Ehsanullah Hamidi’s role in revealing the scandal was not immediately clear, and he was not referenced in The Guardian’s story.
“Afghanistan’s intelligence agency must immediately release these human rights defenders,” Amnesty campaigner Samira Hamidi said in a statement.
“They are at risk of torture and other ill-treatment. Rather than punishing them for speaking out against these horrific crimes, the authorities should praise them for their work.”
Logar provincial governor spokesman Didar Lawang confirmed Mahmudi’s arrest.
“He was arrested after the people of Logar asked the government to arrest him and question him about a paedophile ring in schools,” Lawang told AFP news agency.
Mahmudi told Amnesty he had received death threats from people accusing him of “dishonouring the people of Logar”.
Afghan officials did not respond to requests for comment on the detentions.
Sexual abuse is widespread in Afghanistan despite efforts to clamp down on the crime, and boys are often reluctant to come forward in a culture that still shames victims rather than going after perpetrators.
Parts of Afghanistan still tolerate the practice of bacha bazi, or “boy play”, where older men force boys to dress up as women, dance, and then force them to have sex.