Laboratory analysis of the oil samples showed they were not from the Malaysia Airlines jet but were a type of fuel used by ships, the Maritime Enforcement Agency said in Kuala Lumpur.
The area became a focus for frantic international search efforts for the Boeing 777 after the large tongues of oil were found in the water on Saturday, hours after the plane dropped off the radar.
In a day of conflicting information which deepened relatives’ anguish, initial reports of debris off southern Vietnam were ruled out, before an aircraft spotted another object which appeared to be a life raft.
Malaysia said it was sending ships to investigate the raft sighting, but a Vietnamese vessel that got there first found only flotsam in the busy shipping lane.
“When we reached the site we recovered only a mouldy cable reel cover,” Vietnamese army deputy chief of staff Vo Vo Tuan told AFP.
“I think there was only one suspect floating object there,” he said, conceding the amount of rubbish floating in the sea made it hard to be “100 percent sure” the ship had reached the location of the reported raft.
Anger mounted amid a scramble for answers, and China – which had 153 of its nationals on board – said Malaysia needed to “step up” its efforts after authorities admitted they were mystified by the disappearance of Malaysia Airlines (MAS) flight MH370.
Beijing’s state media lashed out at Malaysia and MAS over their handling of the crisis that began when the jet vanished early Saturday an hour after leaving Kuala Lumpur bound for Beijing.
“The Malaysian side cannot shirk its responsibilities,” the Global Times newspaper, which is close to the ruling Communist Party, wrote in a scathing editorial. “The initial response from Malaysia was not swift enough.”