Among the 25 US special operations forces killed in Wardak province were 22 Navy SEALS, considered to be the "best of the best", US military official said Sunday. In the single deadliest loss for US troops since the Afghan war began in late 2001, 30 service members died early Saturday when a helicopter carrying them went down while they were reinforcing other troops. Insurgents are believed to have shot down the CH-47 Chinook, the official said. The Taliban claimed militants downed the helicopter with a rocket-propelled grenade. The majority of the Navy SEALs who died belonged to the same covert unit that conducted the raid that killed Osama bin Laden in May, though they were not the same men, the (CNN) quoted the military official as saying. The troops died during a "quick reaction" mission to assist military personnel pinned down by insurgents in a fierce firefight. Saturday''s NATO crash killed more than two dozen US troops, making it the war''s deadliest single incident for Americans, according to a CNN count. Reflecting on the sobering loss, US President Barack Obama said the deaths were "a reminder of the extraordinary sacrifices made by the men and women of our military and their families, including all who have served in Afghanistan." NATO''s International Security Assistance Force said 30 US service members in ISAF, one civilian interpreter and seven Afghan commandos were killed. The nationality of the interpreter was not known late Saturday. The US deaths came as NATO is drawing down and handing over security control to national forces. Some 10,000 US troops are scheduled to depart by year''s end, with all US military personnel out of Afghanistan by the end of 2014. However, no one is talking about withdrawing special operations forces and they are expected to stay on the job. "We are determined to stay the course, especially in this crucial period when Afghan and international security forces are working closer than ever to make transition a success," NATO Secretary-General Anders Fogh Rasmussen said. Special operations forces have been conducting almost daily night-time raids against insurgent targets in rugged areas like Wardak. The Chinook went down as an Afghan and coalition force operation targeted a bomb-making cell leader in Wardak, leading to the detention of numerous insurgents Friday, according to ISAF. It is not clear if the helicopter incident and the raid were connected. Mohammad Hazrat Janan, head of the provincial council, said Tangi village elders reported that insurgents shot at the craft when it was returning from an operation. ISAF has not said how the incident occurred. Spokesman Justin Brockhoff acknowledged the helicopter had been flying in an area where there was reported insurgent activity.