KABUL, Afghanistan — At least 19 Afghan civilians were killed Wednesday when their minibus struck a roadside bomb in southern Helmand province, provincial officials said. The dead included seven women and five children.

The incident occurred in Sangin district, about 30 miles northeast of Lashkar Gah, the provincial capital. The bus was carrying Afghans from Lashkar Gah to Sangin, said Daud Ahmadi, a spokesman for the provincial governor.

NATO officials have said that violence largely has diminished in Helmand, where Afghan forces have begun to take over responsibility for security in some areas from U.S.-led international forces. The incident came a day after a suicide attack killed 55 Shiite Muslim worshipers in Kabul on the holiest day of the Shiite calendar.

Haji Abdul Wahab, a tribal chief in Helmand who knew the bus driver, said of the man: "He wanted to fuel up his car, and just before he turned (into) the fuel station, he hit the bomb."

Another five civilians were wounded in the attack.

Three districts in Helmand have been nominated for the second phase of the security transition. The districts of Nad Ali, Nawa and Marjah have been the focus of conflict in past years.

President Hamid Karzai condemned the attack Wednesday. He also canceled a trip to London after Tuesday's mosque bombing and visited some victims of that blast at a hospital in Kabul.

(Safi is a McClatchy special correspondent.)

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