Afghan officials say four girls were killed by a roadside bomb in the country's south as they way on their way home after being sent out to fetch water.

Helmand governor's spokesman Ummar Zawaq says the girls, aged 10 to 12 years, were on their way home in the provincial capital of Lashkar Gah when the bomb went off on Thursday morning.

Violence this year has matched its worst levels in nearly 12 years of war. According to the most recent figures from the Interior Ministry, 180 civilians were killed across Afghanistan last month.

The Ministry of Defense says 11 Taliban militants were killed in two different operations in the province of Lowgar, just south of Kabul, and seven others were wounded. One Afghan soldier was also killed.