Protesters on Monday also reportedly stoned a passing convoy of US-led coalition vehicles, but the US military said none of its personnel were injured.
Khalid Pashtun, spokesman for the Kandahar provincial governor, blamed "enemies of the government and the coalition" for stirring up what started as a peaceful protest. Three unidentified armed men were arrested and are under questioning, he said.
About 1000 people had gathered to demand authorities provide better security in the city, after a series of kidnappings, including that of a 12-year-old boy who was killed recently by his abductors although relatives had paid a ransom.
Pashtun said outsiders infiltrated the protest, and then demonstrators smashed car windscreens, stoned and looted shops and hotels, and ransacked government offices, including one of the Women's Affairs Ministry.
An Afghan official said the rally
was infiltrated by outsiders
He said coalition soldiers whose vehicles had been stoned opened fire in the air to scare off protesters, but in Kabul, a top US commander, Maj. Gen. Eric Olson, said the coalition was neither the target of the protest nor involved in putting it down.
Pashtun said seven policemen, five security guards and five demonstrators were injured in the melee and by stone-throwing, and one boy suffered a broken leg when he was hit by a coalition vehicle.
Police restored order after about three hours, and now the city is calm, he said.
US forces hunting Taliban and al-Qaida members have a base in Kandahar, the main city of southern Afghanistan.