The military in Pakistan denies reports that weapons fire from its side of the border provoked a NATO airstrike which killed at least 24 Pakistani soldiers early on Saturday.
The Army says reports from Afghan and Western officials that NATO was reacting to gunfire from the Pakistani side of the border are untrue.
Afghan officials quoted in The Wall Street Journal said the attack was called in to shield NATO and Afghan forces who were under fire while targeting Taliban fighters.
One official quoted in the paper said Kabul believes the fire came from an army base.
Military sources earlier told the BBC in Paktika province in Afghanistan that a US-Afghan special forces mission had been in the area where a Taliban training camp was believed to be operating.
They said the mission came under fire from a position within Pakistan and they received permission from the NATO's ISAF headquarters to fire back.
Pakistan describes the incident as a violation of its sovereignty and the mandate of the international forces in Afghanistan.
The incident took place at the Salala checkpoint, about 2.5km from the Afghan border, about 2am local time on Saturday.
The Pakistani army said helicopters and fighter aircraft hit two border posts about 300 metres apart.