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

The downing, in which seven Afghan commandos were also killed, 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 Friday night 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.