The Taliban are increasingly targeting civilians seen to be co-operating with the government, raising fresh concerns about the prospects for peace in the country after most foreign troops pull out next year.
Afghan President Hamid Karzai condemned the killings, with a swipe at neighbouring Pakistan which he has been visiting for two days.
"The killing of innocent engineers and workers shows the Taliban and their foreign masters want Afghanistan to be a impoverished and underdeveloped country forever," he said, in an apparent reference to Islamabad.
In Herat, one of Afghanistan's most stable provinces whose small but promising private sector is driving the national economy, the Taliban kidnapped and killed four engineers and two trainers, governor Fazlullah Wahidi said.
The men, all Afghan, worked for a World Bank-funded programme created by the Karzai government that aims to improve local project management.
The killings came within hours of the discovery of the bodies of six drivers in the eastern province of Paktia.