The bomber struck as the men came out of the Kandahar compound of the USPI security company, said Rohullah Khan, an official with the company. Three others were wounded, he said.
The area where the attack happened is located opposite the Canadian Provincial Reconstruction Team inside Kandahar city. The blast was the sixth suicide attack in Kandahar province in the last nine days.
Provincial police chief Asmatullah Alizai said two foreigners, four Afghan policemen and a translator were killed.
USPI employee Mohammad Aszal said the two foreign victims were American.
Qari Yousaf Ahmadi, who claims to be a spokesman for Taleban affairs in southern Afghanistan, contacted The Associated Press and said the militant group was responsible for the attack. Ahmadi's exact ties to the militants are not known.
Near-daily attacks plague Afghanistan's lawless southern provinces — the former stronghold of the hardline Taleban regime, where the central government wields little power.
Taleban militants have launched a record number of suicide and roadside bombs this year. A growing insurgency, especially in the country's south and east, has left close to 4,000 people dead.
Despite the spike in suicide bombings in the past 10 days, NATO said Wednesday that the overall number of coordinated insurgency attacks across the country has decreased.
The number of major attacks in November was 449, a drop of nearly 50 percent compared to 869 in September, said Brig. Richard Nugee, the chief NATO spokesman in Afghanistan.
As the number of attacks on NATO and Afghan troops decreased, militants have resorted to suicide bomb attacks, Nugee told a news conference in Kabul.
"By using suicide bombs, they are being forced into a desperate tactic which in the long run will work against them because the people of Afghanistan will go against them," he said.