NATO said Sunday it was probing the Taliban\'s claim that they shot down a helicopter, killing a team of 30 American troops, many of whom were special forces, and seven Afghan commandos. An interpreter also died when the Chinook helicopter plummeted after a firefight with insurgents during an anti-Taliban operation late Friday in Wardak province, southwest of the capital Kabul. The crash site had been sealed off by Sunday, with reports that fighting was still going on in the area where a rocket propelled grenade (RPG) is thought to have downed the troop-carrying aircraft. The incident was the biggest single loss of life for foreign forces since an American-led invasion of Afghanistan toppled the Taliban from power in 2001, several weeks after the September 11 attacks in the United States. \"Afghan and foreign troops are still in the area,\" provincial spokesman Shahidullah Shahid told AFP on Sunday.\"The area is sealed off and we have reports of sporadic fighting,\" he said, noting that phone coverage had been blacked out. Chinooks are widely used by coalition forces in Afghanistan for transporting large numbers of troops and supplies around the war zone. Their size and lack of speed makes them especially vulnerable to ground attacks. A witness told AFP the helicopter went down following a raid on a Taliban commander\'s home. The Taliban claimed responsibility for the attack. Local and Afghan army officials said an insurgent rocket felled the helicopter, which was said to have broken into several parts after being hit. The NATO-led ISAF (International Security Assistance Force) mission in the troubled country, confirmed an investigation was under way to determine the exact circumstances of the crash. \"The operation of recovery is ongoing,\" it said in a statement, referring to efforts to reclaim wreckage from the site.An ISAF spokesman would not comment on what attempts were being made to recover the bodies of those killed. US President Barack Obama paid tribute to the troops who died and said the incident was a reminder of the \"extraordinary sacrifices\" made by the men and women of the military and their families. Defense Secretary Leon Panetta vowed the US would \"stay the course\" in Afghanistan despite the latest loss. There are currently around 140,000 foreign soldiers in Afghanistan, with about 100,000 of them from the United States. All international combat troops are due to leave by the end of 2014, but intense violence in recent months, including a series of assassinations in the volatile south, has raised questions about the prospects for Afghan forces. Some foreign troop withdrawals have already begun as part of a transition that has seen local soldiers and police, whose abilities are disputed, take control of key regions this summer. Afghan President Hamid Karzai\'s office was first to officially release the death toll on Saturday and he offered condolences to the victims\' families. US television networks reported that 25 of the dead in Friday\'s attack were Navy SEALs. Sources in the Obama administration told AFP that those killed came from the army, navy and air force, without saying if they were SEALs.The Navy Times, considered a well-informed military journal, said 17 of the dead were SEALs and that 15 them came from Gold Squadron, sometimes known as SEAL Team 6 -- the same unit that killed Osama bin Laden in Pakistan on May 2. The defence ministry in Kabul said the seven Afghan soldiers who were killed were members of an elite commando unit. The previous single biggest death toll for foreign soldiers since military operations in Afghanistan began in 2001 was in 2005, when 16 US troops died when a Taliban rocket hit their Chinook in the eastern province of Kunar. Meanwhile, two French Foreign Legion soldiers were among four NATO troops killed Sunday in two separate insurgent attacks in Afghanistan, the French presidency said.