The Wednesday suicide attack on a mini bus in Kabul ferrying journalists affiliated with Tolo TV, Afghanistan's 24-hour news channel, was an atrocity designed to undermine the country's still-fragile media freedom, it said.
Both the Taliban and an individual who claims to represent a group that affiliates with the Islamic State claimed responsibility for the attack, which killed seven journalists from Tolo TV and its production wing and also injured 25 others including bystanders.
A Pashto-language Taliban statement described the bombing as "revenge" for alleged "false allegations" against the group.
The statement explicitly listed both Tolo TV and its news channel rival 1TV as "military targets" for allegedly serving as "informational warfare tools of the American and Crusading forces".
Human Rights Watch said: "The targeting of journalists reflects a depraved strategy to make media freedom a casualty of the ongoing conflict.
"Designating journalists and other civilians as 'military targets' does not make them so, and deliberately attacking them constitutes a war crime."