New evidence suggests that missing Malaysia Airlines flight MH370 may have been deliberately cut off from the rest of the world.
US officials said that because two separate communication systems were shut down separately, the plane did not suffer a catastrophic accident.
According to data obtained, the reporting system was shut down at 1.07am (Malaysia time) and the transponder at 1.21am.
This suggested that the shut down in communications was deliberate, ABC News aviation consultant John Nance said.
Another US official said that they may have an "indication" of where the missing flight may be located, and have switched focus to the Indian Ocean.
According to a report from ABC News, American military forces were moving the USS Kidd to the area to begin the search.
"We have an indication the plane went down in the Indian Ocean," the senior official was quoted as saying.
According to the unnamed official, there were signs the plane had flown four or five hours after it initially disappeared.
It is believed to be based on the plane "pinging" a satellite.
On modern aircraft, planes "ping" every hour in a system called Airplane Health Management.
However, it's unclear whether this would help pinpoint the location of the missing plane.
However, Malaysian officials moved to hose down that theory, saying that a report the plane had flown on for hours after losing contact was not correct.
They also believed satellite images of suspected debris from a missing jet were yet another false lead.
China had sparked talk of a breakthrough in the riddle of the Malaysia Airlines (MAS) jet with satellite images of three large floating objects near where flight MH370 with 239 people on board lost contact on Saturday, en route from Kuala Lumpur to Beijing.
- No debris at crash site: Malaysia
- Engine data said plane flew five hours: WSJ
- Pilot's last words revealed
- Oil rig worker 'saw plane in flames'
But Vietnamese and Malaysian planes that searched the area in the South China Sea on Thursday found no sign of wreckage of the Boeing 777, which has one of the best safety records of any jet.
The US Navy Seventh Fleet also said that it did not have any evidence to corroborate the reports of debris spotted by the Chinese satellites.
Adding to the confusion, the Wall Street Journal reported that US investigators suspected the plane flew for four hours after its last known contact with air traffic control at 1:30 a.m. Malaysian time, based on data automatically sent from its Rolls-Royce engines.
The WSJ said US counterterrorism officials were probing the possibility that a pilot or someone else on board diverted the jet towards an unknown location after turning off its communication transponder.
But Malaysia denied the report as "inaccurate".
"The last (data) transmission from the aircraft was at 0107 hours which indicated that everything was normal," Transport Minister Hishammuddin Hussein told reporters.
"Rolls-Royce and Boeing teams are here in Kuala Lumpur and have worked with MAS and investigation teams since Sunday. These issues have never been raised."
He added that China had told Malaysia that the satellite photos posted on the website of a Chinese state science agency were released "by mistake and did not show any debris".
Major General Datuk Affendi Buang briefs the media during an update on the missing Malaysia Airlines plane. Photo: Getty.
Every day like eternity
Authorities have chased up all manner of leads, including oil slicks, a supposed life raft found at sea and even witness accounts of a night-time explosion, only to rule them all out.
"Every day it just seems like it's an eternity," Danica Weeks, whose husband Paul was on board, told CNN from their home in the Australian city of Perth.
Fighting back tears, she described how Paul had left his wedding ring and watch with her for safekeeping before starting his journey to a mining venture in Mongolia.
"I'm praying that I can give (them) back to him. It's all I can hold onto. Because there's no finality to it and we're not getting any information," she said.
Malaysia has said that the plane may have turned back after taking off and military radar detected an unidentified object early Saturday north of the Malacca Strait, off west Malaysia, but it is unclear if it was the missing airliner.
The search for the plane now encompasses both sides of peninsular Malaysia, over an area of nearly 27,000 nautical miles (more than 90,000 square kilometres) and involves the navies and air forces of multiple nations. India deployed three ships and three aircraft to the remote Andaman and Nicobar Islands Thursday.
Theories about the possible cause of the disappearance range from a catastrophic technical failure to a mid-air explosion, hijacking, rogue missile strike and even pilot suicide.
Beijing will keep up the search "as long as there is a glimmer of hope", Chinese Premier Li Keqiang said.
The passengers included 153 Chinese citizens, and Li told his once-a-year news conference: "Those people's families and friends are burning with anxiety."
Pursuing all concrete clues
The satellite information prompted the focus of the search to swing back Thursday to the original flight path, after a shift in recent days to Malaysia's west coast.
The China Centre for Resources Satellite Data and Application said in a statement on its website earlier this week that it had deployed eight land observation satellites to scour the suspected crash area.
By Tuesday morning, it had obtained images covering 120,000 square kilometres, describing their quality as "rather good".
China has also requested assistance from a fleet of Earth-monitoring satellites under an international charter designed to aid emergency efforts.
US authorities said their spy satellites had detected no sign of a mid-air explosion.
Malaysian police said Thursday they were investigating the two pilots, although the transport minister denied media reports that their homes had been raided.
Malaysia Airlines has said it was "shocked" over allegations raised in an Australian television report that First Officer Fariq Abdul Hamid, 27, along with a fellow pilot, violated airline rules in 2011 by allowing two young South African women into their cockpit during a flight.
It also emerged that months before the Malaysia Airlines jet vanished, US regulators had warned of a "cracking and corrosion" problem on Boeing 777s beneath their satellite antenna that could lead to a drastic drop in cabin pressure and possible mid-air break-up.
But Gerry Soejatman, a Jakarta-based independent aviation analyst, said the warning did not apply to the missing aircraft, a Boeing 777-200ER, which has a different kind of antenna.
"When an aircraft simply disappears from radar with no trace whatsoever, normally it means a rapid deterioration of the aircraft -- an explosion or structural failure that's very rapid," he added.
"That means the wreckage would be found near where it was last reported. But in this case, this doesn't seem to be the case."
On Thursday, Malaysia Airlines said it would retire the flight codes MH370 and MH371 -- the return flight from Beijing to Kuala Lumpur -- as a mark of respect.