JOIN USA minibus ran over a bomb in Nahri Sarraj district of Helmand province, with the blast killing all 18 passengers, said Kamaluddin Sherzai, the province's deputy police chief.
"The mine was very powerful and destroyed the vehicle," he said. "They were all civilians. Some were children."
Another civilian was killed and four were wounded when the farm tractor they were riding in struck a mine in Garmser district, Sherzai added.
Police who responded to the minibus explosion came under fire from insurgents, but there were no casualties among the policemen.
However, Sherzai said three Afghan policemen died in a fight with insurgents yesterday night in Helmand's Gereshk district.
In its midyear report, the United Nations said the number of Afghan civilians killed in war-related violence rose by 15 percent in the first half of 2011.
The report said 1,462 Afghan civilians lost their lives, including 444 killed by roadside bombs. During the first half of last year, 1,271 Afghan civilians were killed in the war.
Violence has been on the rise as insurgents try to regain territory lost last fall and winter to the US-led coalition in southern Afghanistan.