Search planes found no sign on Thursday of a missing Malaysia Airlines aircraft in an area where satellite images had shown debris, taking the as-yet fruitless hunt into the sixth day.
Adding to the deepening mystery surrounding the fate of the plane and 239 people on board, the Wall Street Journal reported on Thursday that U.S. investigators suspect the aircraft flew for about four hours after reaching its last confirmed location under conditions that remain murky.
At the same time, China heaped pressure on Malaysia to improve its coordination over the search for the Boeing 777, which disappeared early on Saturday on a flight from Kuala Lumpur to Beijing. Of the 239 people on board, up to 154 were Chinese.
Premier Li Keqiang, speaking at a news conference in Beijing, demanded that the "relevant party" step up coordination while China's civil aviation chief said he wanted a "smoother" flow of information from Malaysia, which has come under heavy criticism for its handling of the disaster.
Vietnamese and Malaysian planes scanned waters where a Chinese government agency website said a satellite had photographed three "suspicious floating objects" on Sunday. The location was close to where the plane, Flight MH370, lost contact with air traffic control.
Aircraft repeatedly circled the area over the South China Sea but were unable to detect any objects, said a Reuters journalist, who was aboard one of the planes.
One U.S. official close to the plane investigation said the Chinese satellite report was a "red herring".
It was the latest in a series of false signals given to the multi-national search team that has been combing 27,000 square nautical miles (93,000 square km), an area the size of Hungary, for the Boeing 777-200ER.
On Wednesday, Malaysia's air force chief said military radar had traced what could have been the jetliner to an area south of the Thai holiday island of Phuket, hundreds of miles to the west of its last known position.
His statement followed a series of conflicting accounts of the flight path of the plane, which left authorities uncertain even which sea to search in for Flight MH370.
The last definitive sighting on civilian radar screens came shortly before 1:30 a.m. on Saturday, less than an hour after the plane took off from Kuala Lumpur, as it flew northeast across the mouth of the Gulf of Thailand.
What happened next remains one of the most baffling puzzles in modern aviation history and the differing accounts put out by various Malaysian officials have drawn criticism of their handling of the crisis.
"The Malaysians deserve to be criticized – their handling of this has been atrocious," said Ernest Bower, a Southeast Asia specialist at the Center for Strategic and International Studies in Washington.
Rodzali Daud, the Malaysian air force chief, told a news conference on Wednesday that an aircraft was plotted on military radar at 2:15 a.m., 200 miles (320 km) northwest of Penang Island off Malaysia's west coast at the northern tip of the Strait of Malacca.
But there has been no confirmation that the unidentified plane was Flight MH370, Rodzali said, and Malaysia was sharing the data with international civilian and military authorities, including those from the United States.
"We are corroborating this," he added. "We are still working with the experts."