Provincial police chief General Abdul Qayuum Baqizoi told Press TV on Saturday that the blast took place in the restive Chak district of the province, situated about 80 kilometers (50 miles) southwest of the Afghan capital Kabul, on Friday afternoon.
The bomb went off when a line of vehicles passed by the area after an inauguration ceremony of a development project.
“Only one vehicle was blown up causing the casualties but other officials from the district escaped unhurt,” Shahidullah Shahid, a spokesman for the provincial government, said.
The Taliban immediately claimed responsibility for the attack, but put the death toll at seven.
Roadside bombs and improvised explosive devices (IEDs) are by far the most lethal weapon the Taliban militants use against Afghan forces, foreign troops, and civilians.
The homemade explosives accounted for half of the about 1,500 civilian deaths in the first six months of last year, according to the United Nations.
Insecurity continues to rise across Afghanistan despite the presence of some 130,000 US-led forces in the war-torn country.
The United Nations announced on February 4 that 2011 was the deadliest year on record for Afghan civilians. The death toll for the civilians rose eight percent compared to the year before and was roughly double the figure for 2007.
—Agencies