Searchers preparing to resume the underwater hunt for Malaysia Airlines Flight 370 increasingly suspect that some of the signals detected last month didn't come from the jetliner's "black-box" flight recorders, a senior Australian naval officer said.

The doubts—based on further acoustic analysis of the transmissions by Australian authorities over recent weeks—represent another potential setback in the two-month-old operation. (Follow the latest developments on Malaysia Airlines Flight 370.)

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