Kabul, Afghanistan (CNN) -- In the single deadliest loss for U.S. 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, officials said.
Insurgents are believed to have shot down the CH-47 Chinook, a U.S. military official said. The Taliban claimed militants downed the helicopter with a rocket-propelled grenade.
Among the 25 U.S. special forces killed in Wardak province were 22 Navy SEALS, considered to be the "best of the best." Seven Afghan troops also died.
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 military official said.
The troops died during a "quick reaction" mission to assist military personnel pinned down by insurgents in a fierce firefight, a U.S. military official told CNN.
DEADLIEST DAYS IN AFGHANISTAN
Saturday's NATO crash killed more than two dozen U.S. troops, making it the war's deadliest single incident for Americans, according to a CNN count. Here are previous large-scale losses.
There are 150,000 ISAF forces in Afghanistan, including nearly 100,000 from the United States -- the largest NATO presence in the region since the U.S.-led war began in 2001.