Suspected ISIL fighters killed at least six Afghan employees of the International Committee of the Red Cross (ICRC) who were carrying supplies to areas hit by deadly snowstorms, according to government officials.
Another two employees were unaccounted for after Wednesday's attack in the northern Jowzjan province, said ICRC spokesperson Thomas Glass, adding that the group did not know who was responsible for the attack.
"Devastated by this news out of #Afghanistan," Peter Maurer, ICRC president, said on Twitter. "My deepest condolences to the families of those killed - and those still unaccounted for."
ICRC put its activities in the country on hold following the attack, the group's global operations head Dominik Stillhart said, "because we need to understand what exactly happened before we can hopefully resume our operations".
Lotfullah Azizi, Jowzjan's governor, told Reuters news agency the aid workers were in a convoy that was carrying supplies to areas hit by avalanches when they were targeted by fighters belonging to ISIL, or the Islamic State of Iraq and the Levant group.
"Daesh is very active in that area," Azizi said, using an alternate name for ISIL, also known as ISIS, which has made limited inroads in Afghanistan but has carried out increasingly deadly attacks.
Rahmatullah Turkistani, Jawzjan police chief, said the workers' bodies had been brought to the provincial capital.
A search operation was launched to find the two missing aid workers.
Zabiullah Mujahid, Taliban spokesperson, told Al Jazeera the group was not involved in the attack.
Al Jazeera's Qais Azimy, reporting from Kabul, said the attack was "one of the few incidents" in the country's north carried out by ISIL, which has been mainly active in the east.
"It's going to be another challenge for Afghanistan security forces," our correspondent said. "They are already fighting the Taliban in that part of the country. Now, a new group is emerging in the north."
Aid workers in Afghanistan have increasingly come under attack amid a surge in violence in recent years.
Speaking from Geneva, ICRC spokeswoman Marie Claire Feghali told Al Jazeera that the organisation makes contact "with all the groups that are active on the ground" to ensure safety before carrying out humanitarian work.
"We do not know why our convoy was attacked," she said.
"Our colleagues were on a humanitarian mission to deliver assistance in Jowzjan ... [Our] team there would have made all the contacts and they were in clearly marked ICRC cars."
In January, a Spanish ICRC employee was released less than a month after he was kidnapped by unidentified attackers in northern Afghanistan.
That staff member was travelling with three Afghan colleagues between Mazar-i-Sharif and Kunduz on December 19 when the attackers stopped the vehicles. The other Afghan ICRC staff were immediately released.
In a recent summary of its work in Afghanistan last year, the ICRC said increasing insecurity had made it difficult to provide aid to many parts of the country.
"Despite it all, the ICRC has remained true to its commitment to the people of Afghanistan, as it has throughout the last 30 years of its continuous presence in the country," the statement said.
In April 2015 the bullet-riddled bodies of five Afghan workers for the Save the Children charity were found after they were abducted in the southern province of Uruzgan.
Source: Al Jazeera and news agencies