Six Afghan employees of the Red Cross were killed by militants suspected to belong to Islamic State.
The victims were delivering relief supplies in Afghanistan's northern state of Jowzjan when they were shot dead.
Two other Red Cross workers are missing.
"This is a despicable act," said Monica Zanarelli, head of the International Committee of the Red Cross in Afghanistan.
"Nothing can justify the murder of our colleagues and dear friends."
Although no militnt group has claimed responsibility, local police blame IS fighters.
"Daesh fighters are active in the area," he said, using the Arabic acronym by which IS is commonly known in Afghanistan.
"We had previously repeatedly warned them not to go to such dangerous areas under Daesh control."
Turkistani said the bodies of the six workers had been brought to a provincial hospital.
Some of them had multiple bullet wounds and had been shot from close range in the head and chest, Fraidoon Habib, director of the hospital, told AFP.
The brazen attack comes at a time when Afghanistan is in dire need of humanitarian assistance, with more than 100 people killed in recent avalanches and tens of thousands displaced by the wrenching conflict.
Red Cross in Afghanistan has suspended its operations but has not withdrawn its staff.
"We now need to analyse what happened, and we will then make our decisions as to how we are going to move forward," Dominik Stillhart, ICRC's director of operations, told AFP.
"The humanitarian situation in Afghanistan is dire. We are one of the few organisations that is present throughout the country, and we will do everything we can to maintain our response in Afghanistan."
ICRC president Peter Maurer denounced the killings as a "huge tragedy", saying it appeared to be a deliberate attack on the charity's staff.
"These staff members were simply doing their duty, selflessly trying to help and support the local community," Maurer said.
Aid workers in Afghanistan have increasingly become casualties of a surge in militant violence in recent years.