KUALA LUMPUR, Malaysia - Malaysian officials, faced with mounting frustration over the progress of their investigation of an airliner that disappeared 10 days ago, made an international appeal Tuesday for help in finding it.

The search has been bedeviled by scant information and contradictory reports, prompting Chinese Ambassador Huang Huikang on Tuesday to say the Malaysians were "inexperienced and lacking the capacity" to carry out the investigation properly.

Malaysia also has been slow to line up help from other countries, including the United States, that have expertise or information that could speed up the search. Although a group of U.S. crash investigators has been in Kuala Lumpur for more than a week, the nation has not accepted assistance from a team at the FBI's Los Angeles Field Office waiting to depart for Malaysia.

Nor has Malaysia responded to an offer of assistance from a U.S. oceanographic institute, whose expertise in underwater searches helped locate the last major airliner to crash into the sea, Air France Flight 447, which disappeared over the Atlantic in 2009.

But Malaysia is warming to some of these offers, U.S. officials said. A senior law enforcement official said Tuesday that the Malaysian government is starting to cooperate with the FBI and American intelligence agents in the field after a week of rebuffing help.

"Initially, there was a little bit of fog of war. That has cleared," the official said. "They had a hard time pulling this together. Every intelligence agency in the world was beating their door down. I think they were overwhelmed and that has settled a little bit."

In Bangkok, a Thai air force spokesman said that Thai military radar may have spotted Malaysian Airlines Flight MH370 just as it steered away from its intended path and after its transponder was cut off. But Air Vice Marshal Montol Suchookorn said officials did not share the information because Malaysia did not specifically request it, the Associated Press reported.

Had Thailand's disclosure come earlier, it might have directed the search away from the Gulf of Thailand, which crews combed for seven days on the theory that the airliner, with 239 passengers and crew members on board, had perhaps crashed at the same time that it disappeared from civilian radar March 8. The focus of the search now is farther to the west, in particular the Indian Ocean.

Malaysian Defense Minister Hishammuddin Hussein, speaking at a news conference Tuesday, brushed off criticism that his government has held back information or been slow to follow possible leads. He said Malaysia is cooperating with the FBI and other international law enforcement authorities.

"Our priority has always been to find the aircraft," he said. "We would not withhold any information that could help. But we also have a responsibility not to release information until it has been verified by the international investigation team."

He added, "Over the last two days, we have been recalibrating the search for MH370. It remains a significant diplomatic, technical and logistical challenge."

Hishammuddin asked the United States on Tuesday to scrutinize data from defense satellites and airborne radar. He also requested more U.S. vessels in the Indian Ocean.

"The entire search area is now 2.24 million square nautical miles," he said. "This is an enormous search area. And it is something Malaysia cannot possibly search on its own."

Unless floating debris from the aircraft is discovered somewhere in that vast area, it becomes increasing unlikely that the plane will be found, U.S. experts said.

In what has become the largest search on record for an aircraft, Malaysia acknowledged for the first time that other countries needed to take leading roles in scouring a grid about the size of Australia. Malaysia said it has divided that grid into 14 sections and negotiated for Australia, China, Indonesia and Kazakhstan to coordinate efforts in some of those areas.

If the plane or wreckage is located, the senior U.S. law enforcement official said, the FBI is ready to dispatch additional teams of agents. They could help with forensic analysis of bodies, debris and other material to help determine what happened. The official said the FBI also is prepared to look into the backgrounds of all the passengers and crew members, but has not been asked by the Malaysian National Police, which is leading the investigation.

"The Malaysians have the lead on this and we stand ready to assist in any way we can," the official said.

At the White House, one senior administration official said cooperation with the Malaysian government is proceeding as smoothly as can be expected given the "unusual" nature of the mystery.

"This is very difficult for any country," the official said, referring to the Malaysian response. "We've provided a lot of technical assistance in particular, and we helped with the new search area."

At the National Security Council, officials are monitoring the response from the Defense and State departments, the National Transportation Safety Board, and the FBI, and the staff has had "working level" meetings with various agencies. But the effort has been based out of the U.S. Embassy in Kuala Lumpur, the official said. The United States has added a few staff members to assist at the embassy.

Citing U.S. officials, The New York Times reported Monday that Flight MH370's westward turn away from its route from Kuala Lumpur to Beijing was programmed into the plane's computer system, suggesting that whoever steered the Boeing 777 had technical expertise.

"If this turn point was loaded in on the ground before takeoff, then both pilots would have to agree on that being part of the flight plan, which is unlikely," said Ron Carr, a retired airline pilot who teaches at Embry-Riddle Aeronautical University in Arizona. "It would be easier and less likely to call attention to a 'not authorized waypoint' for it to be loaded 1/8after takeoff 3/8 when the course change is to be conducted."

Although Malaysian authorities have appealed for help with the underwater search, they have not responded to offers from the Woods Hole Oceanographic Institute in Massachusetts, which found Air France Flight 447.

"We've tried every way we can at Woods Hole just to have a conversation with someone in Malaysia," said Dave Gallo of Woods Hole. "We offered through our State Department, and then we tried to go directly to the Malaysians and to Boeing. Nothing."

Gallo said that if the plane is underwater, searchers first must find evidence of its location by spotting debris on the surface.

"It's similar to finding a needle in a haystack, which is doable these days if you have the right tools," he said. "So knowing that we're at least looking in the right haystack is important. We don't want to be looking in the Gulf of Thailand in shallow water and then they say it's off the coast of Perth 1/8Australia 3/8 in deep water."

Five days after the Air France crash, floating debris was located. Using water currents and the final communications from the aircraft, investigators narrowed the search area to 40 square miles.

Brought into the search after the plane's locator box stopped sending underwater signals, the Woods Hole team found the Airbus A330 more than 11,000 feet below the surface, almost two years after it went down.

The longer it takes to find floating evidence of Flight MH370, the more problematic the search becomes. Narrowing the area to scour would allow ships towing sonar sleds on long tethers to focus on that section before the 30-day battery life runs out on an underwater beacon emitting homing signals every second.

As time passes, floating debris drifts and disperses. Experts can evaluate those patterns based on the time the material has been in the water and pinpoint where to search. If the search narrows from millions of square miles to just a few dozen, it becomes a matter of bringing in the right equipment.

Ships towing sonar sleds must move at less than two miles an hour or risk breaking the miles-long line that lets their equipment sink thousands of feet below the surface. The better choice is autonomous underwater vehicles (AUVs) - unmanned mini-submarines that can work near the ocean bottom.

"They have the ability of running very precise lines on the sea floor, just like plowing a field or mowing the lawn," said Gallo, whose team also mapped the remains of the Titanic ocean liner on the bottom of the Atlantic.

Gallo said assembling a fleet of AUVs, if a search area can be narrowed, is a challenge.

"They are scattered all over the Earth," he said. "There are a couple of companies that can respond. There are a couple of oceanographic institutes like ourselves that can respond, but no one's got dozens of vehicles. Everyone's got one or two, and who knows where they are?"

If that focus comes down to the waters off Perth, he said, that is "one of the most incredibly complicated underwater terrains on the planet."

"This place is not only rugged, but it's unpredictable," he added. "It can be a high plateau, a deep valley, a mountain slope, so it's difficult."

Australia said Tuesday that it will take several weeks to search its area, with help coming Wednesday from New Zealand and the United States. That search area - the southernmost potential crash spot for the aircraft - is 230,000 square miles, about the size of Wyoming.

Halsey reported from Washington. Washington Post staff writers Tim Craig in Islamabad, Pakistan; Annie Gowen in New Delhi; and Ernesto Londono, Adam M. Goldman, Scott Higham and David Nakamura in Washington contributed to this report.