KABUL, Afghanistan — At least 19 Afghan civilians were killed by a road side bomb on Wednesday in southern Helmand province as a mini bus drove over it, Daud Ahmadi, spokesman for provincial governor, said.

Seven women and five children were among the dead.

No one has claimed responsibility for the bomb. Insurgents often use improvised explosive devices (IEDs) to target Afghan and foreign forces.

The incident occurred in Sangin district, about 50 kilometers to the northeast of Lashkar Gah, the provincial capital.

The minibus was carrying Afghan civilian passengers from Lashkar Gah to Sangin district when the explosion took place, said Ahmadi.

Haji Abdul Wahab, a tribal chief in Helmand knew the driver of the minibus and recalled his name as Shakir.

"He wanted to fuel up his car and just before he turned into fuel station, he hit the bomb," said Haji Abdul Wahab.

Five other civilians wounded in the attack were taken to an International Security Assistance Force (ISAF) health facility, Ahmadi said.

Three districts in Helmand &mdash: Nad Ali, Nawa and Marja — are nominated for the second phase of transition. These districts have been the focus of conflict in the past years.

The attack comes a day after 55 people werekilled in a suicide blast in Kabul, most of them Shi'ite Muslims.

(Ali Safi is a McClatchy special correspondent.)