KUALA LUMPUR, Malaysia » Planes sent Thursday to check the spot where Chinese satellite images showed possible debris from the missing Malaysian jetliner found nothing, Malaysia’s civil aviation chief said, deflating the latest tantalizing lead in the six-day hunt.

"There is nothing. We went there, there is nothing," Azharuddin Abdul Rahman told reporters in Kuala Lumpur.

The Wall Street Journal, meanwhile, reported that U.S. investigators suspect the plane flew on for four hours once it lost contact with air traffic controllers, based on data from the plane’s engines that are automatically downloaded and transmitted to the ground as part of routine maintenance programs.

The report raises questions as to why the Boeing 777 would have been flying without contact, and if anyone would have been in control during that time. U.S. counterterrorism officials are considering whether a pilot or someone else on board intentionally disabled the jetliner’s transponders to avoid detection and divert it, the report said.

The hunt for the missing Malaysia Airlines flight 370 has been punctuated by false leads since it disappeared with 239 people aboard about an hour after leaving Kuala Lumpur for Beijing early Saturday.

The plane was heading northeast over the South China Sea when it disappeared, but authorities believe it may have turned back and headed into the upper reaches of the Strait of Malacca or beyond.

Chinese satellite imagery showed possible debris is not far from where the last confirmed position of the plane was between Malaysia and Vietnam. The images and coordinates were posted on the website of China’s State Administration of Science, Technology and Industry for National Defense.

China’s state Xinhua News Agency said the images from around 11 a.m. on Sunday appear to show "three suspected floating objects" of varying sizes in a 12-mile radius, the largest about 79-by-72 feet off the southern tip of Vietnam.

Li Jiaxiang, chief of the Civil Aviation Administration of China, said later China had yet to confirm any link between the suspected floating objects and the plane.

Pham Quy Tieu, deputy transport minister, told The Associated Press that the area had been "searched thoroughly" by forces from other countries over the past few days. Doan Huu Gia, chief of air search and rescue coordination center, said Malaysian and Singaporean aircraft were scheduled to visit the area again Thursday.

Malaysia has come under some criticism for its handling of the search, which currently covers 35,800 square miles and involves 12 nations.