"A vehicle belonging to a non-governmental organisation has been attacked by unknown armed people," Baghdis provincial police chief Amir Shah Naibzada told AFP.

"In an attack on a Medecins Sans Frontieres vehicle two Afghans and three foreigners have died."

"It is too early to say who is responsible for this attack," he added.

Naibzada said the aid workers were killed by two men, one armed with a Kalashnikov and the other with a pistol.

"Three foreigners -- one woman and two men -- have died. Two Afghans, one a translator and the second a driver also died," he added.

Naibzada said he was on his way to the site in the Khair Khana area of Qades district of Baghdis some 500km west of Kabul.

The incident was confirmed by several Western humanitarian sources who said the non-governmental agency concerned was Medecins Sans Frontieres (Holland) which works in Baghdis and neighbouring Herat province.

A spokesman for Medecins Sans Frontieres, or "Doctors Without Borders", in Kabul refused to comment on the incident.

Provincial governor Azizullah Hafzali confirmed the incident which occurred at 4:00 pm (1130 GMT) and said the aid workers were from Medecins Sans Frontieres, an aid agency which works to bring medical assistance to war zones and impoverished nations.

"Five people, three expatriates and two Afghans were killed by unidentified people," he said.

An Afghan security source speaking on condition of anonymity told AFP that among the dead are two Afghans, a Belgian woman, a Dutchman and a Norwegian man.

A spokesman for the Belgian embassy in Kabul refused to comment.

While a wave of low-level guerrilla insurgency has hit southern and southeastern Afghanistan, the north is generally considered safe.

Attacks against soft targets such as aid workers have been concentrated mainly in the south, the former stronghold of the Taliban regime.