A Briton and a South African working for international courier company DHL where killed along with an Afghan guard in a shoot out in Afghanistan's capital Kabul on Saturday, officials 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 on Monday in a killing claimed by the 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, without giving their identities.

The British embassy said later they were a Briton and a South African.

The foreigners worked for DHL, said a spokesperson in Berlin for the German post office, which owns the international courier. Afghan police said they were the Kabul director and deputy director of the company.

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.

"He was a very nice guy. He was a good friend of mine. What's going on here?" said bystander, Walid Osman, a friend of one of the dead foreigners.

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 in a western suburb of Kabul, said the SERVE Afghanistan aid organisation for which she worked.

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

Authorities have not confirmed that the assassination was carried out by the Taliban. The Afghan government urged foreign nationals and aid workers afterwards to review their security.

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

AFP