A Briton and a South African working for international courier DHL were killed along with an Afghan guard in a shoot-out in Afghanistan's capital Kabul on Saturday, officials and the company said.

It was the second fatal shooting involving the international community in the city in five days with a dual national British-South African aid worker gunned down Monday in a killing claimed by the insurgent Taliban.

It was unclear what prompted Saturday's exchange of fire outside the DHL offices, but one senior police official said an argument had erupted between the foreigners and some Afghans and it was not a Taliban attack.

"Two foreigners and one Afghan have been killed," said Kabul deputy police chief Alishah Ahmadzai. Two people were also wounded, he said.

DHL later on Saturday named the victims as Briton David Giles and South African Jason Bresler, adding its Kabul operation had been closed and an investigation launched.

The company declined to say what positions the pair held, but Afghan police earlier said one was the Kabul director and the other the deputy director.

One of them was shot dead in the front passenger seat of a four-wheel-drive vehicle, said an AFP reporter who saw his body slumped in the seat. The front side window was shattered and the cabin spattered with blood.

The other was in the back seat, according to a policeman. The vehicle was covered with a plastic sheet so witnesses could not see inside.

The Afghan appeared to have been shot outside the vehicle, where blood was pooled. He was a guard, a police witness said.

Several people were detained afterwards for questioning, police said.

The killing comes after 34-year-old aid worker Gayle Williams was shot dead Monday while she was walking to work at the SERVE Afghanistan aid organisation.

The Islamist Taliban claimed she was killed because SERVE was "preaching Christianity," a charge rejected by the group which works to help disabled Afghans.

"That is simply not true," Serve Afghanistan spokesperson Rina van der Ende reiterated at an emotional press conference in Kabul attended by Williams' mother and sister ahead of her funeral on Sunday.

"There is still no clue why Gayle was murdered," she said.

Authorities have not confirmed that the assassination was carried out by the Taliban.

Security has plummeted in the country this year, with insurgent attacks and crime both surging as foreign troops fight to stem the Taliban-led insurgency.

AFP