Two Americans and four Afghans died when a suicide bomber blew himself up outside the compound on Wednesday, witnesses said.
Three others were wounded, an official said.
The bomber attacked as the men came out of the compound of a US security company in Kandahar, Rohullah Khan, a company official, said. The Pakistan-based Afghan Islamic Press said the bomber set off his explosives among a crowd of people standing outside the office waiting to go in to work.
Akhtar Mohammad, a USPI employee, said among those killed was the head of the company's Kandahar office, who he identified as Mr Jack, AIP reported.
The blast was the sixth suicide attack in Kandahar province in the last nine days.
The area where the attack happened is opposite the Canadian Provincial Reconstruction Team inside Kandahar city.
Almost 4,000 people have been killed in the increasing violence across Afghanistan this year.
Almost 4,000 people have been killed in the increasing violence across Afghanistan this year.
