The Taliban had threatened an Afghan reporter who was killed in a car bomb attack this week for investigating their attacks, Human Rights Watch said.
Radio Liberty reporter Aliyas Dayee, 33, was killed on Thursday when a sticky bomb attached to his car exploded in the southern city of Lashkar Gah, the scene of intense fighting in recent months.
Dozens of other journalists had also been threatened by the group, the US-based rights group said in a statement late Thursday.
Targeted killings of prominent figures, including journalists, clerics, politicians and rights activists, have become more common in recent months as violence surges in Afghanistan, despite ongoing peace talks between the government and the Taliban.
No group has so far claimed the killing of Dayee.
But Dayee recently told HRW that he had received death threats, warning him to stop his reporting on Taliban military operations, it said.
"The Taliban had searched his house, questioned him about his movements, and asked local residents to report on his behaviour," journalists who knew Dayee told HRW, the statement added.
"The night before he was killed, Dayee had emailed a colleague saying he believed his life was in danger."
Helmand province -- a Taliban stronghold where Lashkar Gah is located -- has seen heavy clashes in recent weeks between the insurgents and government forces.
Dayee had been "explicitly" warned not to report on the Taliban's operations in the province or that the group was "violating the agreement" it signed with Washington in February, that paved the way for withdrawing American forces from Afghanistan, HRW said.
The rights watchdog said dozens of Afghan journalists have been threatened by the Taliban in recent months.
"The killing of Aliyas Dayee simply for doing his job sends a chilling message to the Afghan media that reporting on the Taliban puts them in grave danger," Patricia Gossman, associate Asia director at HRW, said.
"This brutal killing of a journalist is nothing more than a cold-blooded execution and raises serious doubts about the protection of free expression in any peace deal with the Taliban," she continued.
Dayee's murder comes after Yama Siawash, a former Afghan television presenter, was killed on Saturday in a similar bomb attack in Kabul.
The two murders come amid surging violence across Afghanistan, much of it unleashed by the Taliban as they attempt to gain leverage in seemingly stalled peace talks in Qatar.