The guards had been protecting a road construction company in Kunar province, a troubled region on the Pakistani border, according to Governor Fazlullah Wahidi.
He said he could not say who might have been behind the attack but Taliban militants waging a bloody insurgency against the Kabul government have been blamed for a string of similar incidents.
Taliban rebels are trying to topple President Hamid Karzai's government and force out tens of thousands of international soldiers based in the country.
