Malaysia’s civil aviation chief has said the fate of a missing Malaysia Airlines jet remains “a mystery”.
Azharuddin Abdul Rahman said officials had not ruled out hijacking as a cause of the plane’s disappearance.
The possible sighting of a yellow life raft was investigated on Monday, but was found to be an unrelated object.
Malaysia Airlines flight MH370 vanished from radar almost three days ago en route to Beijing from Kuala Lumpur, with 239 people on board.
Relatives of the missing passengers have been told to prepare for the worst.
Malaysia’s armed forces chief also said they were co-operating with Chinese intelligence to identify the two passengers on board flight MH370 who were travelling on stolen passports.
Malaysia’s acting transport minister, Hishamuddin Hussein, said all of the relevant information concerning those two passengers had now been passed on to the various national intelligence agencies which were investigating the matter.
Earlier, China said the Malaysian authorities needed to “step up their efforts” to find the missing jet which had more than 150 Chinese nationals on board.
“The Malaysian side attaches importance to the incident with a sincere attitude, but in light of the situation, the Malaysian side needs to step up their efforts,” a Chinese foreign ministry spokesman told reporters at a regular news briefing, the AFP news agency reports.
Commander William Marks from the US Seventh Fleet, which is taking part in the search, says he expects the plane’s flight recorders to be floating in the water.
“In calm seas, if there were a soccer ball [football] or a basketball floating in the water, the radar could pick it up. They [flight recorders] typically have a radio beacon and so for example our P3 [radar] – if they are flying within a certain range of that – will pick up that radio beacon. We have not yet picked up anything, but that’s typically what those black boxes contain.”
There are now 40 ships and 34 aircraft from nine different nations taking part in the search in the seas off Vietnam and Malaysia.
Late on Sunday, the Vietnamese authorities said two objects had been sighted in waters south of Vietnam which appeared to resemble aircraft parts, including a door.
The debris was in a similar area to a possible oil slick seen by Vietnamese navy planes on Saturday.