NATO gunship helicopters attacked a checkpost in Pakistan's northwest tribal area of Mohmmand Agency which borders Afghanistan on Saturday morning, killing 25 Pakistani security personnel and injuring 15 others, reported local state-owned TV channel PTV.

Local government-run TV channel PTV said that 25 Pakistani security personnel including two officers were killed and some others injured when NATO gunship helicopters shelled an army checkpost in the Salala village of Banezai town in Mohmmand Agency.

At least seven of the injured people in the attack are in serious condition, said PTV, adding that the injured have been airlifted by helicopter to a hospital in Ghalanai, capital town of Mohmmand Agency.

Earlier local media reports said that Pakistan's army mouthpiece Inter-Service Public Relations (ISPR) has confirmed the NATO air strike, but ISPR did not say how many NATO helicopters were involved in the attack and how many people got killed and injured.

The cross-border airstrike by NATO troops in Afghanistan into the Pakistani side is a serious violation of the Pakistani space territorial rights and such strikes have also occurred in the past.

"The NATO attack is an attack on Pakistan's sovereignty," said Barister Masood Kausar, Governor of Khyber Pakhtunkhwa, a province in northwest Pakistan. He said that the government should take a serious notice of the violation.

Chief Minister of Punjab Province Shahbaz Sharif also condemned the NATO attack, according to local media reports.

Latest news coming in said that the Pakistani acting ambassador to the United States Iffat Gardezi has already lodged a protest to the U.S. side. She warned that such attacks would affect U.S.- Pakistan relations.

(Xinhua contributed to the story)