The attacker detonated himself in a market place in Ghazni province, two days after another bomber struck outside government buildings in the north of Afghanistan killing 14 people including a provincial politician.
"At around 5:00 pm, a 18-year-old suicide attacker blew himself up in a market in the district of Muqur," Ghazni province deputy governor Mohammad Ali Ahmadi told AFP.
"As a result, four anti-Taliban fighters and three civilians were killed and 14 others injured."
Local army spokesman Nazifullah confirmed the incident and death toll to AFP.
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The Taliban launched their annual "spring offensive" last month vowing to use suicide blasts to inflict maximum casualties and warning Afghans working for President Hamid Karzai's regime to distance themselves from the government.
All NATO combat missions will finish in Afghanistan by the end of 2014 and foreign troops have already begun to withdraw from the battlefield as Afghan police and army take over the fight against the insurgents.
Also today, officials said that unknown gunmen dragged the father of Afghanistan's cricket captain from his car on the outskirts of Jalalabad city and have taken him hostage.