Gulam Mohammad Tahiri, an Afghan army intelligence officer, said the 12 killed included seven policemen, three soldiers and two officials with the national spy agency.
He says the killings took place yesterday in Andar district and that the Taliban forced local residents to watch the killings.
Tahiri says all 12 had been abducted at different times.
He says insurgents would stop cars on the road between Paktika province and the capital, Kabul, and snatch passengers.
Taliban gunmen are increasingly staging ambushes on provincial highways as they step up their war, now in its 15th year, against the Kabul government.