Insurgents shot down a U.S. military helicopter during fighting in eastern Afghanistan, killing 30 Americans, most of them belonging to the same elite unit as the Navy SEALs who killed al-Qaeda leader Osama bin Laden, as well as seven Afghan commandos, U.S. officials said on Saturday. It was the deadliest single loss for American forces in the decade-old war against the Taliban.

The downing was a stinging blow to the lauded, tight-knit SEAL Team 6, months after its crowning achievement. It was also a heavy setback for the U.S.-led coalition as it begins to draw down thousands of combat troops fighting what has become an increasingly costly and unpopular war.

None of the 22 SEAL personnel killed in the crash were part of the team that killed bin Laden in a May raid in Pakistan, but they belonged to the same unit. Their deployment in the raid in which the helicopter crashed would suggest that the target was a high-ranking insurgent figure.

Special operations forces, including the SEALs and others, have been at the forefront in the stepped up strategy of taking out key insurgent leaders in targeted raids, and they will be relied on even more as regular troops pull out.

The strike is also likely to boost the morale of the Taliban in a key province that controls a strategic approach to the capital Kabul. The Taliban claimed they downed the helicopter with a rocket while it was taking part in a raid on a house where insurgents were gathered in the province of Wardak overnight. Wreckage of the craft was strewn across the crash site, a Taliban spokesman said.

A senior U.S. administration official in Washington said it appeared the craft had been shot down. The official spoke on condition of anonymity because the crash is still being investigated.

The U.S.—led coalition said in a statement that 30 American service members, a civilian interpreter and seven Afghan commandos were killed when their CH-47 Chinook crashed in the early hours on Saturday. A current U.S. official and a former U.S. official said the Americans included 22 SEALs, three Air Force air controllers and a dog handler. The two spoke on condition of anonymity because military officials were still notifying the families of the dead.

Afghan President Hamid Karzai announced the number of people killed in the crash and offered his condolences to the American and Afghan troops.

The deaths bring to 365 the number of coalition troops killed this year in Afghanistan and 42 this month.

The overnight raid took place in the Tangi Joy Zarin area of Wardak’s Sayd Abad district, about 60 miles (97 kilometres) southwest of Kabul. Forested peaks in the region give the insurgency good cover and the Taliban have continued to use it as a base despite repeated NATO assaults.

Taliban spokesman Zabiullah Mujahid said in a statement that the helicopter was involved in an assault on a house where insurgent fighters were gathering. During the battle, the fighters shot down the helicopter with a rocket, he said.

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