"Their vehicle was ambushed and five people died on the spot," and one other person was still missing, he said on Thursday.
Two people had also been injured in the incident which happened on Wednesday afternoon in Ozbin village of Kapisa province.
The victims were working for the Swedish Development Fund which was assisting the Ministry of Rural Development in implementing a National Solidarity Programme partially funded by the World Bank.
The programme aims to assist Afghan communities manage their own reconstruction and development projects.
The deaths come less than two weeks after four Afghan men working for a demining organisation were shot dead when their vehicles were ambushed in southwestern Farah province, bordering Iran.
Rumsfeld in Kabul
Meanwhile, US Defence Secretary Donald Rumsfeld arrived in Afghanistan on Thursday amid stepped up American and Pakistani operations against al-Qaida and Taliban militants.
Rumsfeld flew into the former Taliban stronghold of Kandahar in the south of the country and will travel on to Kabul, winding up a week-long tour of Iraq and Central Asia.
He is due to meet US military commander in Afghanistan, Lieutenant-General David Barno, and Afghan President Hamid Karzai during his half-day visit.
US officials said they would discuss long-term security plans for Afghanistan, still racked by violence blamed on guerrillas, including remnants of the ousted Taliban militia and al-Qaida fighters.
Hunt for bin Ladin
More than 550 people, including many rebels, have been killed since August.
In Kandahar, Rumsfeld visited a Provincial Reconstruction Team, one of about a dozen civilian-military teams deployed across the country in a bid to improve security in remote regions as well as help the US military gather intelligence.
The US military appears increasingly confident of finding al Qaida chief Usama bin Ladin and other senior militant figures this year.
A US military official spoke on Wednesday of a "renewed sense of urgency" in the hunt for bin Ladin, and Pakistan launched a fresh operation on its side of the Afghan-Pakistan border during which it detained about 20 suspected militants.