The explosion hit a passenger bus on Herat-Kabul, Head of Health Department of Farah Province Abduljabbar Shayeq told the Islamic Republic News Agency (IRNA).
He said that some of the wounded people are in critical condition, meaning that the death toll may increase.
Bomb explosion is the main cause of civilian death in Afghanistan, according to a United Nations report.
The terrorist group of Taliban has been blamed for the newest explosion.
The group has not commented on the incident yet.
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