Two officers a major and a captain were among those killed when the helicopters targeted the check post at Baizai area of Mohmand tribal region last night, state-run PTV reported.
Fifteen more personnel were wounded and the death toll could rise as some of the injured were in a serious condition, the TV channel reported. In retaliation, Pakistani authorities stopped container trucks carrying supplies for US and NATO forces in Afghanistan, it said.
A brief statement from the Inter-Services Public Relations said International Security Assistance Force and NATO helicopters "carried out unprovoked and indiscriminate firing" on a Pakistani check post in Mohmand Agency.
The fresh border incident comes in the wake of already strained Pak-US ties that deteriorated over unilateral American raid that killed Osama bin Laden in May and over accusation that Pakistan intelligence was involved in a September siege of the US embassy in Kabul. US considers the tribal belt a hotbed of al-Qaeda and other militants who plot attacks on American forces in Afghanistan.
After the attack, Pakistani security forces blocked all entry points to Mohmand Agency and began checking all vehicles entering the area, TV news channels reported.