The International Committee of the Red Cross (ICRC)has suspended operations in Afghanistan after gunmen killed six employees helping deliver emergency relief to a remote northern region hit by heavy snow storms.
The governor of Jowzjan province said the aid convoy was attacked by gunmen suspected to be from the so-called Islamic State group.
The head of the ICRC called the incident the "worst attack against us" in 20 years, but the charity said it did not know who was responsible.
A search operation was under way to find two charity workers who were still missing.
"As we speak our operations are on hold indeed, because we need to understand what exactly happened before we can hopefully resume our operations," ICRC director of operations Dominik Stillhart told Reuters in Geneva.
Afghanistan is the ICRC's fourth largest humanitarian programme in the world, Mr Stillhart said.
The attack follows a warning by the charity last month that mounting security issues made it perilous to deliver aid to large swathes of the country.
A massive snowstorm dumped as much as two metres of snow on areas of Afghanistan over the weekend, according to officials, killing more than 100 people.
Lotfullah Azizi, the Jowzjan provincial governor, said the aid workers were carrying livestock supplies to areas badly affected by the storm.
"Daesh is very active in that area," he said, using an alternative name for Islamic State, which has made limited inroads in Afghanistan but has carried out increasingly deadly attacks.
The ICRC team included three drivers and five field officers.
Jowzjan police chief Rahmatullah Turkistani said the workers' bodies had been taken to the provincial capital.
"These staff members were simply doing their duty, selflessly trying to help and support the local community," ICRC president Peter Maurer said.