Herat governor Sayed Wahid Qitali said an overnight bomb explosion targeted a police outpost near 13th district of Herat city.
The provincial police said two military personnel were wounded in the explosion.
Other sources, however, said casualties were likely to be more.
There was no claim of responsibility for the attack.
Nearly a month ago an explosion targeted a security outpost in Pul-e Malan area of Herat province, injuring three policemen.
The government blamed the Taliban for the attack.
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