WASHINGTON—The number of Americans applying for first-time unemployment benefits fell last week, a sign of a firm labor market.

Initial jobless claims, a measure of how many workers were laid off across the U.S., decreased by 6,000 to a seasonally adjusted 216,000 in the week ended June 15, the Labor Department said Thursday. Economists surveyed by The Wall Street Journal had expected 220,000 new claims.

Estimates...