No group has claimed responsibility for the blast, but the city's military commander blamed it on the ousted hardline Islamic Taleban movement.

The blast took place in the commercial centre, near hotels and a bazaar often used by foreigners, but all the injured were Afghan civilians, police say.

On Wednesday, a US soldier was injured in a grenade attack in the same area.

There have been no reports of fatalities following Saturday's explosion, which took place shortly before 1300 local time (0830 GMT), apparently after a bomb was left on a bicycle.

Sensitive moment

The blast comes at a sensitive time, with elections going on for representatives to a loya jirga, or grand council, to debate and ratify a new constitution for Afghanistan, the BBC's Lyse Doucet in Kandahar says.

The Taleban have threatened to step up attacks to disrupt the elections.

Rumsfeld said the Taleban will not return to power

But other groups have also been carrying out attacks, she says.

Saturday's explosion blew metal doors off three nearby shops and sent shattered glass flying.

The area was cordoned off after the explosion, but life has now returned to normal there.

Police commander Mohammad Hashim blamed the attack on "the enemies of the government," referring to Taleban militants who are continuing a violent campaign in the south and east of the country.

Kandahar was a stronghold of the Taleban, who were ejected by US-backed Afghan forces two years ago.

Saturday's bombing comes less than a month after a car bomb exploded outside a UN office in the city. There were no injuries in that attack.

Visiting Afghanistan earlier in the week, Donald Rumsfeld, the US defence secretary, said the Taleban will not return to power in the country.