The International Committee of the Red Cross suspended operations in Afghanistan after gunmen killed six employees helping to deliver emergency relief to a remote northern region hit by heavy snowstorms.
The governor of Jowzjan Province said the aid convoy was attacked by suspected Islamic State gunmen. The head of the Red Cross called the incident the "worst attack against us" in 20 years.
A search operation was under way to find two charity workers who were still missing late on February 8.
"Our operations are on hold, indeed, because we need to understand what exactly happened before we can hopefully resume our operations," the charity's director of operations, Dominik Stillhart, said.
Afghanistan hosts the Red Cross's fourth-largest humanitarian program in the world, Stillhart said, and the attack follows a warning by the charity last month that mounting security issues are making it perilous to deliver aid to large swaths of the country.
"The humanitarian situation in Afghanistan is dire. We are one of the few organizations that is present throughout the country, and we will do everything we can to maintain our response in Afghanistan," he said.