Kabul, Dec 6 (DPA) At least five Afghans and three American citizens were killed Wednesday when a suicide bomber blew himself up in front of a private US security firm in Afghanistan's Kandahar city.

The bomber wore a vest fitted with explosives and detonated himself in front of the office of the US Protection and Investigations (USPI) firm, an interior ministry spokesperson said here.

The Americans killed included USPI security chiefs in Kandahar and the western province of Herat.

The Afghans who died also worked for the security firm, the ministry said. Among the projects the Texas-based USPI is involved in is providing security at construction sites at Kandahar.

Violence has been on the rise this year in Afghanistan, particularly in the south, and over 100 suicide attacks have been reported so far, according to the NATO-led International Security Assistance Force.

Over 230 Afghans and 17 foreign military personnel have died in these bombings, apart from those killed Wednesday.