Four civilians have been killed by a bomb hidden inside a cart at a livestock market in southern Afghanistan, a provincial official said.

Jawed Faisal, a spokesman for the governor, said 10 other people were injured in the blast in the city of Kandahar. It was not clear what the bomb was targeting.

Violence has escalated in recent months, with insurgents trying to take advantage of the transfer of security responsibility from foreign to Afghan forces as the international coalition withdraws from Afghanistan.

As a result, the UN has said, civilian casualties rose dramatically in the first six months of 2013.