Pakistan's army has lodged a strong protest and demanded talks with NATO commanders after an allliance helicopter hit a Pakistani checkpoint, injuring two security personnel.
"It [the incursion] happened early morning," a Pakistani intelligence official, who declined to be identified because he was not authorised to speak to the media, told the Reuters news agency.
"The helicopter hit a Pakistani checkpoint on the border in the Datta Khel area."
A Western military official in Kabul, told Reuters that two NATO helicopters supporting a base in eastern Afghanistan had returned fire after being attacked from Pakistan.
Pakistan's military said it had sought a meeting with NATO commanders over the incursion, which came a day after US senator John Kerry met Yusuf Raza Gilani, Pakistan's prime minister, amid tensions in the country's relations since the killing of Osama bin Laden earlier this month.
Pakistan has condemned the US for conducting that operation in violation of its national sovereignty.
Tuesday's incident came hours before Yusuf Raza Gilani, the Pakistani prime minister, arrives in China on a visit seen by some as a diplomatic effort to seek closer and more productive ties with another major power.