The attack occurred in the Mir Mundo area of Helmand province, 50 miles northwest of Kandahar (search), said Mohammed Wali Khan, a spokesman for the governor of Helmand.
Helmand Governor Sher Mohammed Akhundzada (search) was not traveling with his guards, who were all government soldiers.
No arrests have been made and no one has claimed responsibility. Security forces later found a car which was apparently abandoned by the attackers, Khan said.
He did not provide further details but said that "this attack was carried out by the Taliban."
Taliban and Al Qaeda (search) rebels have been launching increasingly bold assaults in recent months, raiding police stations, killing aid workers and confronting U.S. troops in growing numbers.
While there are 5,500 NATO (search)-led peacekeepers in Afghanistan, they are restricted to the capital, Kabul. An additional 11,500-member U.S.-led coalition is also present in the country and is focused on battling Taliban and Al Qaeda insurgents.
President Hamid Karzai's administration is trying to build a national army that would eventually have 70,000 troops and maintain security throughout the country. But training is slow and the fledgling force has no more than 5,000 soldiers.
The Taliban militia was ousted by a U.S.-led coalition in late 2001 for harboring terrorists. Its fighters, however, are believed to be regrouping and stepping up deadly attacks.
In an ambush on Wednesday, suspected Taliban attackers sprayed a pickup carrying three Afghan aid workers with bullets, killing an engineer for a local aid group and wounding his driver, in Ozikhushk area of Helmand.
Two men have been arrested in the ambush, officials said Sunday.