The family were travelling to Lashkar Gah, the main town in Helmand province, when they were killed, provincial spokesman Daud Ahmadi said.
"Four children, one female, and one male were killed in the sedan car en route to (the provincial) capital," he added.
Although the attack bore the hallmarks of the Taliban, who frequently plant roadside bombs in Afghanistan`s restive regions such as Helmand, the militant Islamist network declined to comment on the attack.
Civilians are the biggest casualties in the near 10-year war in Afghanistan, where 150,000 foreign forces are stationed, although some withdrawals are due to start next month.
The United Nations says Afghan civilian deaths in the war increased 15 percent to a record high of 2,777 last year. More than three-quarters of the dead were killed in violence blamed on insurgents. (*)
Editor: Kunto Wibisono
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