PESHAWAR - The officials have confirmed that shots were fired against the United States gunship helicopters in the border areas of South Waziristan near Angoor Adda on Monday, but they denied the involvement of Pakistani troops in it. "Neither the US choppers violated Pakistani air space, nor Pakistani troops were involved in firing against these choppers," remarked a spokesman of Inter- Services Public Relations (ISPR) to TheNation on Monday. However, Major Murad of ISPR confirmed that choppers were sighted in Afghanistan territory across the border. As per details, from two to four US gunship helicopters were sighted near Angoor Adda, area of South Waziristan Agency close to Pak-Afghan border, late on Sunday evening. At that time, they said, one US B-52 fighter was also on air patrolling in the area. The local tribesmen informed that soon after witnessing the US choppers in the area, Pakistan's security forces gave the "danger sirens." After sirens, firing was heard and the US choppers returned to their base inside Afghanistan. Major Murad of ISPR, when contacted, said that US choppers, including Chinook, were sighted across the border in Afghanistan. These choppers made no violation of Pakistani air space. Similarly, he also confirmed firing against the US choppers but said that Pakistani security forces were not involved in it. He said that they were unaware as to who opened the firing against the US choppers. The local tribesmen also informed about air patrolling by several US gunship helicopters in Macha Dad Kot, a village on Pak-Afghan border opposite to South Waziristan Agency. Agencies add: Shots were fired when US-led coalition helicopters based in Afghanistan neared the border with Pakistan, officials said Monday, but there were conflicting accounts of the incident. Security officials said the threat of an incursion Sunday led Pakistani troops and tribesmen to fire their weapons, but both the Chief Pakistan Army spokesman and the US-led coalition denied any such incident took place. The gunfire broke out about 100 metres from the South Waziristan tribal area, where Al Qaeda and Taliban fighters are believed to be sheltering. There were no casualties. "The US-led coalition troops in helicopters came close to the border and they tried to sneak into Pakistan territory but shots were fired by Pakistani troops and the coalition troops retreated," a local security official said. A military official based in the area initially confirmed to AFP that an incident took place. "There was firing but our troops were not involved," he told AFP. "Firing was heard but there was no violation of Pakistan territory," he said. A second security official in the area said tribesmen joined in the firing after Pakistani soldiers played bugles to alert local people to the threat of an incursion. But the Pakistan army's chief military spokesman, Major-General Athar Abbas, denied there had been any such incident late Sunday. "These reports are not correct," he said. "We have checked, there is an FC (Frontier Corps) post in the area. No helicopter came inside our side of the border, nor did our troops fire at any," Abbas added. The US-led coalition, based in Bagram, Afghanistan, said they were not aware of Sunday's incident. "Our helicopters do fly close to the border conducting routine missions, but none have attempted to cross into Pakistan. We have no reports of such events," an official in the media office said. Separately, US drones have carried out repeated missile strikes killing dozens of people, including civilians, in Pakistan and straining the relationship between the "war on terror" allies. BBC reported Pakistani troops have fired shots into the air to stop US troops crossing into the South Waziristan region of Pakistan, local officials say. Reports say nine US helicopters landed on the Afghan side of the border and US troops then tried to cross the border. The confrontation began at around midnight, local people say. They say seven US helicopter gunships and two troop-carrying Chinook helicopters landed in the Afghan province of Paktika near the Zohba mountain range. US troops from the Chinooks then tried to cross the border. As they did so, Pakistani paramilitary soldiers at a checkpoint opened fire into the air and the US troops decided not to continue forward, BBC reported quoting local Pakistani officials say. Reports say the firing lasted for several hours. Local people evacuated their homes and tribesmen took up defensive positions in the mountains. The incident happened close to the town of Angoor Adda, some 30km from Wana, the main town of South Waziristan. A Pakistani military spokesman in Islamabad confirmed that there was firing but denied that Pakistani troops were involved.