A homicide bomber blew himself up outside a compound for security contractors in southern Afghanistan on Wednesday, killing two Americans and four Afghans, a company official and witnesses said.

The bomber attacked on foot as the men left the Kandahar city compound of the Houston-based security company USPI, said Rohullah Khan, an official with the company. Three others were wounded, he said.

The blast, the sixth suicide attack in Kandahar province in nine days, went off opposite the offices of the Canadian Provincial Reconstruction Team, a military team charged with rebuilding efforts in the area.

A Canadian military spokesman earlier said that one foreigner and two Afghans were killed. He could not be reached to confirm the new toll.

Near-daily attacks plague Afghanistan's lawless southern provinces — the former stronghold of the hard-line Taliban regime where the central government wields little power.

Taliban militants have launched a record number of homicide and roadside bombs this year. The growing insurgency, especially in the country's south and east, has left close to 4,000 people dead.