Afghan police say a roadside bomb blast has killed at least 11 civilians in southern Helmand province.

Authorities say the victims were killed Friday morning when their minivan ran over a bomb in the Nahri Sarraj district.

On Thursday, a group of suicide bombers attacked several government buildings in central Afghanistan, killing at least 19 people and wounding 37 others in one of the deadliest attacks to hit the country in recent months.

The Taliban claimed responsibility for the coordinated attack in Tarin Kot, the capital of Uruzgan province. The group said it used a team of six suicide bombers to strike at the governor's house, police headquarters and the base of a militia commander who provides security to NATO convoys.

A recent United Nations report says violence against Afghan civilians has risen by 15 percent in the first half of the year, with more than 1,400 civilian deaths.