A roadside blast ripped through a civilian vehicle in southern Afghanistan on Tuesday, killing four people and wounding six others, a government spokesman said.

The bomb exploded in Nad Ali district of Helmand province on a road also used by government drug-eradication forces, said Daud Ahmadi, a spokesman for Helmand's governor.

Ahmadi blamed the Taliban and the drug mafia for planting the bomb.

Southern Afghanistan is the center of the Taliban-led insurgency. Helmand province is also the world's largest producer of opium, the main ingredient in heroin. Millions of dollars from the illicit drug trade fund the insurgency.

After the blast, five new bombs were found on the same road, forcing the drug eradication team to temporarily suspend its operation in Nad Ali, Ahmadi said.