Missing Malaysia Airlines Plane: Investigators Keep Focus on 'Deliberate Act'

March 22, 2014— -- American investigators have settled on three primary theories to explain the disappearance of Malaysia Airlines Flight 370, a senior U.S. official told ABC News tonight.

The leading theories are:

1. Pilot suicide or other human action;
2. Fire or catastrophic mechanical malfunction;
3. Terrorism.

With terrorism all but ruled out, however, investigators still are leaning toward the vanishing of the passenger jet with 239 travelers and crew aboard as "a deliberate act," the official said.

"That's pretty much what everyone thinks," the senior U.S. official, who receives frequent updates on the investigation, told ABC News.

Get All the Latest Updates on the Vanished Malaysia Airlines Plane

The Obama administration has been cautious all along in the sparse public statements they have made over the past two weeks, beyond pledging to assist the Malaysian government.

Asked about lithium batteries known to be aboard MH370, the official said the amount and weight of the potentially flammable cargo "has been classified" secret by investigators but said it was "comparable to the Dubai jet," referring to UPS Flight 6, which crashed in the United Arab Emirates in late 2010.

Still, the focus of the probe, as ABC's Brian Ross was told a week ago by another senior official, remains primarily on what happened inside the cockpit rather than in the cargo hold, noting that the aircraft is believed to have flown more than seven hours after taking off from Kuala Lumpur on March 7.

Finding out what happened to the jet and how it vanished seemingly into thin air must be determined by the U.S. in order to ensure it isn't repeated or becomes a national security vulnerability, the official added.

The official spoke after the Chinese government released a satellite image showing a new object floating in the water today, another lead for search crews trying to find the missing plane.

WATCH: New Satellite Images Reveal Possible Objects in Indian Ocean

China's State Administration for Science, Technology and Industry for National Defense released the photo of the object, which is reportedly 74 feet long and 43 feet wide. It was spotted about noon Tuesday in the southern Indian Ocean, about 75 miles southwest of the region where two objects released by Australia were previously seen.

The news of the object interrupted a press conference Malaysian officials held, as Malaysia's Acting Transport Minister Hishammuddin Hussein was given a piece of paper containing details about the object. He concluded the press conference early as reporters peppered him with questions about the development.

Before receiving the note, Hishammuddin told reporters that China, India, Pakistan, Myanmar, Laos and Kyrgyzstan hadn't found anything related to the plane in the northern search corridor.

Malaysia Airlines Flight 370 disappeared on March 8.

Search crews again came up empty during the third day of the search in the desolate southern Indian Ocean. There was no reports of any sign of the missing plane or the two objects spotted by satellite in the area six days ago.

The search area covered Saturday, an area of 36,000 square kilometers, included the area where the new object was spotted by Chinese satellites but the object wasn't found, according to the Australian Maritime Safety Authority.

Satellite images released by Australia showed two objects – the biggest about 80 feet long – in the southern Indian Ocean. Those images were taken March 16, but the search in the area did not start until Thursday, March 20, because it took time to analyze the images.

During a news conference, Truss questioned whether the delay meant search crews missed their chance to find the objects.

"The fact that it's six days ago that this imagery was captured does mean, clearly, what objects that were there are likely to have moved a significant distance as a result of currents and winds. It's also possible of course that they've just drifted to the bottom of the ocean bed," he said.

Truss remained optimistic about the search efforts.

"It is a very remote area, but we intend to continue the search until we're absolutely satisfied that further searching would be futile. And that day is not in sight," he said.

Aircraft in the Indian Ocean included two ultra-long-range commercial jets and four P3 Orions, the Australian Maritime Safety Authority said.

Because of the distance to the area, the Orions will have enough fuel to search for two hours, while the commercial jets can stay for five hours before heading back to the base.

Two merchant ships were in the area, and the HMAS Success, a navy supply ship, was due to arrive late Saturday afternoon. Weather in the search zone was expected to be relatively good, with some cloud cover.

Two Chinese aircraft were expected to arrive in Perth Saturday to join the search, and two Japanese planes will arrive Sunday. A small flotilla of ships from China is still several days away. The Malaysian plane passengers included 154 Chinese.

EXCLUSIVE VIDEO: David Wright Aboard Navy Search and Rescue Plane

Malaysia – which is overseeing the overall search efforts – asked the U.S. for undersea surveillance equipment to help in the search, said Rear Adm. John Kirby, a Pentagon spokesman. Defense Secretary Chuck Hagel promised to assess the availability of the technology and its usefulness in the search, Kirby said.

The Pentagon says it has spent $2.5 million to operate ships and aircraft in the search and has budgeted another $1.5 million for the efforts.