SYDNEY (AFP) - Four acoustic transmissions that have been the focus of the search for missing Malaysia Airlines Flight 370 are no longer believed to have come from the plane's black box, a US official said on Thursday.
The US Navy's deputy director of ocean engineering Michael Dean told CNN there was now broad agreement that they came from some other man-made source unrelated to the jet that disappeared on March 8 carrying 239 people.
He said if the ping-emitting beacons had come from the plane's onboard data or voice recorders they would have been found by now.
"Our best theory at this point is that (the pings were) likely some sound produced by the ship ... or within the electronics of the towed pinger locator," Mr Dean said.
"Always your fear any time you put electronic equipment in the water is that if any water gets in and grounds or shorts something out, that you could start producing sound," he added.
He said it was not possible to absolutely exclude that the pings came from the black boxes, but there was no evidence now to suggest they did.
The US Navy pinger locator, dragged by the Australian ship Ocean Shield, was used by searchers to listen for underwater signals in the remote southern Indian Ocean in an area where satellite data suggested the plane went down.
A series of signals it picked up promoted Australian Prime Minister Tony Abbott to say he was "very confident" they were from the black box from the plane that vanished en route from Kuala Lumpur to Beijing.
It led to the deployment of a US mini-sub to scour the sea bed, but it has failed to find any sign of the jet.
Asked by the broadcaster if the other countries involved in the search - which is being led by Australia - had reached the same conclusions, Mr Dean replied "Yes."