PESHAWAR/ISLAMABAD Nato helicopters from Afgha-nistan wounded at least two Pakistani soldiers in a cross-border attack at a checkpost in North Waziristan Agency on Tuesday morning. Reportedly, two Nato helicopters violated the Pakistan airspace at Admi Kot checkpost in tehsil Datta Khel, prompting the security forces to open fire at them. Two Pakistani troops were injured during the exchange of fire. It has also been reported that Nato helicopters first opened fire at the checkpost and Pakistani troops retaliated. In a statement, the ISPR said two Nato helicopters violated Pakistan airspace at Admi Kot Post, North Waziristan Agency in the early hours of Tuesday. The troops at the post fired upon the helicopters and, as a result of exchange of fire, two soldiers received injuries. Pakistan Army demanded an immediate flag meeting over violation of its airspace by two NATO helicopters. It bears mentioning here that in September last, Pakistan had closed for more than a week the land route for Nato supplies in Afghanistan, when two Pakistani soldiers were killed in a similar border clash in a tribal area. The route was reopened after Nato tendered an apolgy. More than 80 per cent of the essential supplies to the NATO/ISAF troops stationed in Afghanistan go through Pakistan under a special transit facility. Agencies add: The western military official in Kabul, who requested anonymity, told AFP that the two helicopters were in Afghanistan in support of a forward operating base which was receiving fire from across the border of Pakistan. Upon arrival at the scene, one of the helicopters received fire from across the border but didnt immediately return fire. Upon receiving fire a second time, the helicopter returned fire, he added. Pakistani authorities later informed ISAF (the US-led International Security Assistance Force in Afghanistan) that two soldiers had been wounded, he said. A spokesman for the international military alliance in Afghanistan said ISAF had reports of a possible incident. We are looking into it, Lieutenant-Colonel John L Dorrian said. A local government official said two helicopters crossed into North Waziristan and remained for about 10 minutes in the area. The helicopters retreated after Pakistani border forces opened fire, a security official said. A shell struck a mountain nearby and two of our soldiers were wounded by the rubble, the official said.