Federal Reserve officials delivered a modestly more upbeat assessment of the economy Wednesday amid a second-quarter growth rebound and deepening debate inside the central bank about when to start raising interest rates.

U.S. gross domestic product, a broad measure of the nation's output of goods and services, advanced at a seasonally adjusted annual rate of 4.0% in the second quarter, the Commerce Department said Wednesday, a significant rebound from a wintry 2.1% contraction during the first three months of the year.

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