PESHAWAR: An early Saturday morning attack by North Atlantic Treaty Organisation (Nato) helicopters killed at least 24 security personnel and injured 12 soldiers on a Pakistani check post in Salala, which is located in the Tehsil Bayzai area of Mohmand Agency on the Pak-Afghan border , sources said.



Inter Services Public Relations (ISPR) sources confirmed the attack, but could not determine the number of casualties as the interrogation was still underway.



The incident took place in a village of Salala, which is an area bordering the Kunar province of Afghanistan.



At least 40 soldiers were stationed at the check post.



An official on the condition of anonymity told The Express Tribune that there was consistent shelling on the Pakistani check post, which resulted in security forces retaliating.



"The actual number of casualties might rise, as it cannot be determined at the moment," the official said.



The official added that nearby areas were also attacked by the helicopters.



“It is a matter of national security and we are still interrogating it,” said a security official. “The matter will be taken up at the highest level.”



"This is an attack on Pakistan's territorial sovereignty, “said Masood Kasur, the governor of Pakistan's northwestern Khyber-Pakhtunkhwa province. "Such cross-border attacks cannot be tolerated any more. The government will take up this matter at the highest level and it will be investigated."



The situation remained unclear as the political administration did not give any information about the incident.



The incident comes a day after Chief of Army Staff General Ashfaq Pervez Kayani met Commander of Coalition Forces in Afghanistan General Allen Jones to discuss measures of enhancing border control on both sides.



The attack will likely worsen US-Pakistan relations, already at one of their lowest points in history, following a tumultuous year that saw the bin Laden raid, the jailing of a CIA contractor, and US accusations that Pakistan backed a militant attack on the US Embassy in Kabul.



An increase inUS drone strikes on militants in the last few years has also irritated Islamabad, which says the campaign kills more Pakistani civilians in the border area than activists. Washington disputes that, but declines to discuss the drone campaign in detail.



Earlier, it was reported that Nato jets had attacked the border post.