The six who were employed by French orgnisation Acted, were shot dead on Wednesday morning and a colleague was wounded in the northern Afghan problem of
Faryab, local police chief Nabi Jan Mullakhail announced.
They were dragged from their car in the Pashtun Kot district of Faryab province, which borders Turkmenistan, before being gunned down, he said.
He blamed Taliban insurgents fighting international forces and forces loyal to the government of President Hamid Karzai.
The news was confirmed by Faryab development projects chief Mohammad Alem Murad.
Acted released a statement from Paris condemning the killings and correcting an earlier report that the death toll was seven.
"Six Afghan employees were killed following an ambush that targeted a team of seven people. One person was injured," it said. "They were killed in the course of their work to support the developement in the north. We deplore the deaths of our colleagues while they were carrying out their duties."
Acted, which is based in Paris, works on development projects in 31 countries.
It was founded in Afghanistan in 1993 and has 34 projects there, employing 864 local staff and 13 international staff, according to its website.
Although they have reduced the number of attacks on schools and clinics under local pressure, some Taliban regard NGOs, especially foreign ones, as agents of the international intervention that drove them out of power in 2001.