Insurgents shot down a US military helicopter during fighting in eastern Afghanistan, killing 30 Americans, most of them belonging to the same elite Navy SEALs unit that killed Osama bin Laden, as well as seven Afghan commandos, US officials said on Saturday. It was the deadliest single loss for American forces in the decade-old war. 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 US-led coalition as it begins to draw down thousands of combat troops fighting what has become an increasingly costly and unpopular war.