Media reports says the International Committee of the Red Cross (ICRC) suspended operations in Afghanistan on Wednesday after gunmen killed six employees helping deliver emergency relief to a remote northern region hit by heavy snow storms.

Citing the governor of Jowzjan province, Reuters reports that the aid convoy was attacked by suspected Islamic State (IS) gunmen.

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 underway to find two charity workers who were still missing late on Wednesday night.

According to AFP, the ICRC convoy, comprising three drivers and five field officers, came under fire while they were carrying much-needed livestock materials to a remote area badly affected in recent days by heavy snowfall.

A massive snowstorm dumped as much as two meters of snow on areas of Afghanistan over the weekend, according to officials, killing more than 100 people.

“Daesh is very active in that area," the Jowzjan governor Lotfullah Azizi said, using an alternative name for Islamic State, which has made limited inroads in Afghanistan but has carried out increasingly deadly attacks.

Taliban spokesman Zabiullah Mujahid said his group was not involved in the attack and promised that Taliban members would “put all their efforts into finding the perpetrators,” Reuters reported.

“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 program in the world, Stillhart said, and 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.

Gunmen in northern Afghanistan kidnapped a Spanish ICRC employee in mid-December, releasing him nearly a month later.