Deputy provincial police chief Baryalia Basharyar says the attack took place on Wednesday in Faryab province's Almar district.
He says the initial death toll of 10 may rise as the explosion was very powerful. It also wounded scores of people, including several policemen.
No group immediately claimed responsibility for the attack.
Taliban insurgents have stepped up their attacks on Afghan soldiers and police in recent months. U.S. and NATO forces formally ended their combat mission at the end of last year, leaving Afghan security forces in charge of public safety in the country.
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