Three foreign aid workers and two Afghans have been killed in an ambush in the north-west of the country, according to police.
The attack occurred in the village of Khair Khana, in Badghis province, 550 km (340 miles) west of Kabul.
All the victims were staff of international aid organisation Medecins Sans Frontieres and were thought to be setting up a clinic in the area.
The former ruling Taleban has said it carried out the attack.
A spokesman in the Pakistani city of Peshawar said his political grouping was responsible for firing on what he alleged was a United Nations vehicle.
Security experts have confirmed that an ongoing Taleban insurrection, while concentrated in Afghanistan's south and east, had also spilled over to the north-west.
MSF confirmed the five victims worked for them.
The foreign victims were a Belgian woman who was a project co-ordinator, a Dutch male logistician and a Norwegian male doctor.
The Afghan victims were a driver and a translator for the organisation. Three other Afghans in the vehicle escaped unhurt.
Gunmen opened fire on their car as they left their office on Wednesday afternoon, Badghis province police chief Amir Shah Naibzada said.
The vehicle was badly damaged, and shell cases were seen strewn by the roadside.
Mr Naibzada said there were two attackers, one armed with a pistol and the other with a Kalashnikov assault rifle.
There was a lone
tyre track leading away from the scene, suggesting the
attackers fled on a single motorbike.
Taleban rebels have targeted aid workers in the south and east of the country, in what is being seen as an attempt to undermine government efforts at reconstruction.
Correspondents say the continuing violence has cast a shadow over plans for elections in the war-torn country in September.
Suspected Taleban fighters killed two Britons and their Afghan translator in eastern Nuristan province in May while evaluating security for the voter registration process.
Such attacks have not so far been reported in the north, but security there is poor and armed robberies are common.