An oil slick spotted on Sunday by the Vietnamese air force did not come from the burst tanks of missing Malaysia Airlines flight MH370, tests revealed on Monday night.
As yet another sighting of suspected crash debris proved to be a false lead, rescuers remained in the dark as to the fate of the passenger jet and the 239 people on board, which has been missing for almost three days.
Faidah Shuib, spokeswoman for the Malaysia Maritime Enforcement Agency, said tests had shown that the slick spotted had come from a ship.
"The chemical department has confirmed this evening the oil found in Malaysian waters yesterday is bunker oil, and is not used by any aircraft."
The slick, from which the samples were collected, was about 185 kilometres north off Malaysia’s east coast state of Kelantan and just south of the point where air traffic controllers lost contact with the plane, which disappeared en route from Kuala Lumpur to Beijing
Over the last 24 hours search teams have ruled out a number of objects seen floating in the water.
A "yellow object" spotted by the crew of a Vietnamese jet, which it was reported may have been a life raft, turned out to be moss-covered rubbish, dashing hopes of survivors after more than two days of fruitless search.
On Monday afternoon a Chinese coastguard ship detected "two large swathes of oil slick" possibly related to the aircraft, Chinese state broadcaster CCTV said.
Samples of the oil slick were taken for examination, CCTV reported. It was not immediately clear whether it was a separate slick.
Malaysia Airlines flight MH370 vanished after climbing to a cruising altitude of 10,668 metres between Kuala Lumpur and Beijing in the early hours of Saturday.
Search teams have not been able to make any confirmed discovery of wreckage in seas beneath the plane’s flight path.
"The fact that we are unable to find any debris so far appears to indicate that the aircraft is likely to have disintegrated at around 35,000 feet," said the source, who is involved in preliminary investigations in Malaysia.
If the plane had plunged intact from such a height, breaking up only on impact with the water, search teams would have expected to find a fairly concentrated pattern of debris, said the source, speaking on condition of anonymity because he was not authorised to speak publicly on the investigation.
Asked about the possibility of an explosion, such as a bomb, the source said there was no evidence yet of foul play and that the aircraft could have broken up due to mechanical issues.
Boeing, the maker of the 777-200ER, declined to comment and referred to its earlier statement, which said it was monitoring the situation.
The Malaysian source said the closest parallels to the Malaysian Airlines disappearance were the explosion on board an Air India jetliner in 1985 when it was over the Atlantic Ocean, and the Lockerbie air disaster in 1988. Both planes were cruising at around 31,000 feet when bombs went off on board.
Canadian and Indian police have long alleged the Air India bombing was conducted by Sikh extremists living in western Canada as revenge on India for the deadly 1984 assault on the Golden Temple in Amritsar, Sikhism’s holiest shrine.
International police agency Interpol has said at least two of the passengers on board the Malaysian plane, and possibly more, used passports listed as missing or stolen on its database.
"Whilst it is too soon to speculate about any connection between these stolen passports and the missing plane, it is clearly of great concern that any passenger was able to board an international flight using a stolen passport listed in Interpol’s databases," Interpol Secretary General Ronald Noble said in a statement.