The suspects are being held for investigation into illegal arms transport.
Their detention spells the latest trouble for Afghanistan's dozens of private security companies that guard supply convoys, development projects and private businesses.
President Hamid Karzai has ordered all the protection companies shut down by March, to be replaced by a unified government-run protection force.
Police who stopped the contractors' vehicle at a Kabul checkpoint on Tuesday found more than two dozen AK-47 rifles in a metal box covered by a blanket, Ministry of Interior spokesman Sediq Sediqi said. Read More