The Danish Committee for Aid to Afghan Refugees (Dacaar) said the workers were travelling through Ghazni Province, south-west of Kabul, on Tuesday when an armed gang stopped the car.

The aid workers were asked to get out of the vehicle. Four were shot dead, while a fifth escaped with injuries.

Dacaar said two of the men worked for the organisation while three others were local Afghans assisting in a local water supply project.

"The attackers ordered them to get out of the car and then tied their hands," Gorm Pedersen, Dacaar's director in the capital, said. "The attackers then opened fire with AK-47 rifles."

The man who had survived was in a good condition in hospital in Kabul, and had given the authorities details of the ambush, Mr Pedersen said.

Taleban

Dacaar has been present in Afghanistan since 1988, working on water, building and health projects.

Its workers in the southern provinces of Helmand, Kandahar and Uruzgan have now been told to suspend operations temporarily, said a Dacaar spokesman in Kandahar, Samander Khan.

He said it was not clear who had carried out the attacks, although local Ghazni governor Haji Asadullah pointed to Taleban fighters.

"The Taleban stopped the car and killed these aid workers," he told the Associated Press.

Recent clashes

Supporters of the ousted Taleban regime have been blamed for the recent rise in violence in Afghanistan, particularly in the south and east.

In August, two aid workers from the Afghan Red Crescent society were killed in an ambush south-west of Kabul.

In recent days, Afghan government troops and American forces have been carrying out operations in the area against suspected members of the former Taleban.