Kabul, January 31: The Afghan Defense Ministry said in a statement on Tuesday that the blast happened against a military convoy in Bakwa district of Farah province.
Elsewhere in Kandahar and Ghazni provinces, at least three more Afghan soldiers were wounded in attacks on Tuesday.
No group has claimed responsibility for the incidents, but the Taliban militants usually carry out the roadside bomb explosions.
The US invaded Afghanistan in 2001 under the pretext of combating terrorism and toppling the Taliban regime.
However, insecurity continues to rise across Afghanistan despite the presence of thousands of US-led foreign forces in the country.
Washington has turned to negotiations with the Taliban militants after ten years of the US-led war on Afghanistan.
—Agencies