Acoustic transmissions at the heart of the search for missing Malaysia Airlines Flight 370 are no longer believed to have come from the plane's black box, a US Navy official said Thursday.

The Navy's deputy director of ocean engineering Michael Dean told CNN there was now broad international agreement that they came from some other man-made source unrelated to the jet that disappeared on March 8, carrying 239 people.

But the Navy took issue with Dean's comments, which threaten to plunge the marathon and costly search into new confusion and extend the agony of relatives who are desperate for closure.

Dean said if the ping-emitting beacons, detected in early April in the southern Indian Ocean, were from the on-board 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," 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 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.

A US Navy spokesman retorted: "Mike Dean's comments today were speculative and premature, as we continue to work with our partners to more thoroughly understand the data acquired by the towed pinger locator.

"As such, we would defer to the Australians, as the lead in the search effort, to make additional information known at the appropriate time."

The Australian-led Joint Agency Coordination Centre (JACC) made no immediate comment.

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 indicated the plane went down.

A series of signals it picked up prompted Australian Prime Minister Tony Abbott to say he was "very confident" they were from the black box of the plane that vanished en route to Beijing from Kuala Lumpur.

It led to the deployment of a US mini-sub to scour the sea bed, but despite an extensive air, surface and underwater search, no sign of the jet has been found.

Missing forever?

The underwater hunt by the US Bluefin-21 submersible had been due to end on Wednesday, May 28.

JACC officials have previously said that once this happened the operation would move to the next phase involving sophisticated equipment to scan the unmapped ocean bed.

A Chinese survey ship, Zhu Kezhen, is currently mapping areas of the sea floor in preparation for the commercially contracted deep ocean search.

Scott Hamilton, managing director of US-based aerospace consultancy Leeham, said the search should be halted until all data were thoroughly re-examined in light of Dean's comments.

"Do they stop the sea search for now? Probably, pending re-analysing everything," he told AFP.

"If you mean do they stop looking for the airplane entirely and just write it off as missing forever, I would say, not yet. They need to exhaust all analysis.

"I think it will be some time, perhaps years, before they completely throw in the towel."

Many relatives of those on board, who were mostly from China and Malaysia, have voiced frustration over the lack of progress and accused Kuala Lumpur on Wednesday of withholding crucial satellite data.

That came after Malaysia on Tuesday released a 47-page summary of communication logs from the plane recorded by British satellite operator Inmarsat, information relatives had long demanded.

"So much time has passed and nothing has been found, so we doubt that the calculated position of the plane is correct," said Steve Wang, a spokesman for a support group of relatives of the flight's 153 Chinese passengers.

Malaysia insists it is doing all it can in what is an unprecedented situation.

Relying in part on the Inmarsat data, officials believe the jet inexplicably veered off its flight path before crashing into the sea, possibly after running out of fuel.