Mistrust between U.S. and Malaysian air-accident investigators has hampered a multinational probe into the jetliner that went missing three weeks ago, people familiar with the investigation said, with no clear leads emerging about who or what was responsible for its disappearance.

hamper：妨碍，束缚       jetliner：喷气客机

As search ships raced to try to confirm airborne sightings of potential wreckage in the newest search area, officially both sides said cooperation between the two countries is good. But people familiar with both countries' efforts say that isn't always the case.

wreckage：残骸

U.S. investigators say they aren't getting a full flow of information from the Malaysians - - prompting some to complain to headquarters in Washington that they feel relegated to the margins, according to several people familiar with the matter. Malaysian investigators, meanwhile, are wary of information leaks they believe are occurring more regularly among their counterparts from Washington.

relegate：归入，提交              wary of：警觉的，小心翼翼的

With a little more than a week left on the battery life of Malaysia Airlines 3786.KU -2.38% Flight 370's data recorders, known as black boxes, search crews were on their way to the new search zone where five planes had spotted debris potentially related to the plane. Though investigators have determined the Boeing BA +1.01% 777 went down somewhere in the Indian Ocean, based on satellite data, a criminal probe into the flight's disappearance has yielded few clues in the two weeks since the Malaysian government announced its suspicion that a deliberate act brought down the Boeing 777.

debris：碎片，残骸

Twin probes into how and why the plane went down rest largely in the hands of Malaysian police and air-safety officials, and Americans working in Kuala Lumpur are convinced their side is 'mainly getting bits and pieces, rather than a full download from the Malaysians,' said one U.S. official briefed on the investigation. Members of the on-site U.S. contingent are 'vetting all the information they do get, to ensure accuracy,' the official added.

In Malaysia, the government has tight control over the media and leaks of information aren't common. By contrast, some people on the Malaysian side perceive Washington to be full of leaks, particularly in the first few days after the plane vanished March 8.

Last week, Malaysia handed over its most important physical evidence to the U.S. Federal Bureau of Investigation - -pilot Zaharie Ahmad Shah's home flight simulator and computer- -for analysis. But before the FBI analysis was complete or the Malaysian government had a chance to make an announcement, a flurry of media reports from Washington revealed that the bureau hadn't found anything to explain Flight 370's disappearance.

'Washington seems to be a leaky boat,' said one person familiar with the Malaysian investigation. 'It erodes trust.' Nevertheless, this person said concern about the Americans' role isn't seriously impeding the investigation. 'We have been surprised at how many people we have been able to rope into this,' this person said.

Still, according to people familiar with the matter, U.S. aviation officials are operating largely out of the U.S. Embassy in Kuala Lumpur and shuttling to meetings with Malaysian officials- -instead of being based full-time in Malaysian offices alongside local investigators, as would often be the case. The U.S. team includes a handful of investigators from the FAA and National Transportation Safety Board.

The embassy declined to comment on the level of cooperation between the two countries.

Malaysian authorities take pride in having assembled a broad multinational coalition to search the Indian Ocean for the wreckage of the Boeing 777, and in the process ceded some of their authority to direct the hunt. The government has repeatedly sought outside help to locate and eventually try to retrieve remnants of the plane carrying 239 people, asking for everything from satellite imagery to search planes to specialized underwater recovery equipment.

'On the criminal aspect of the investigation, Malaysian police are working very closely with the international agencies,' Defense Minister Hishammuddin Hussein told reporters Friday.

But investigators from the Federal Aviation Administration and Boeing Co. focusing on aircraft performance and systems have expressed concern about poor coordination and information flow, according to people familiar with the matter.

Boeing, without the full involvement of Malaysian investigators, has run some computer models of the last phase of the flight, highlighting another point of tension in the probe, two people familiar with the matter said. These so-called engineering simulations seek to lay out the most likely movements of the plane before and after it is presumed to have run out of fuel. Such work typically would be more closely coordinated with leaders of the overall investigations, according to these people.

Boeing on Friday re-emphasized that it continues to serve as a technical adviser to the NTSB.

An FAA spokeswoman said the agency's 'working relationship with the Malaysian Directorate General of Civil Aviation has been strong for many years and has continued to be strong throughout the investigation.'

The current tensions between U.S. and Malaysian investigators have roots in issues that appeared three weeks ago, people familiar the matter said, soon after the flight dropped off civilian radar March 8 en route to Beijing from Kuala Lumpur.

From the beginning, according to a U.S. government official and others, Boeing was upset that it took about three hours- -much longer than would be typical- -for Malaysian authorities to inform company representatives the jet hadn't been heard from.

Boeing's team remains 'quite frustrated and doesn't trust the process,' according to one person familiar with the company's views.

FAA and NTSB officials didn't play a prominent role in briefing Malaysian Prime Minister Najib Razak just before his somber announcement Monday that Flight 370 'ended in the southern Indian Ocean.' The analysis was based primarily on work done by satellite-operator Inmarsat ISAT.LN +0.07% PLC and the U.K.'s Air Accidents Investigation Branch, the NTSB's British counterpart. Officials in Kuala Lumpur and the AAIB have a long-standing relationship on safety matters.

'The Malaysians have a much closer association with the AAIB' than with the NTSB, according to one person familiar with Malaysia Airlines' operations. 'There is simply a greater comfort level there.'

NTSB spokeswoman Kelly Nantel said 'there is no friction between the U.S. and Malaysian investigators,' adding 'they are all working together, with one common goal.'

friction：摩擦

Malaysian authorities say that background checks have been completed on all passengers by their countries of origin and that no one stands out as a suspect. At the same time, Malaysian and U.S. officials also say they haven't ruled out any potential cause for the plane's disappearance, including the possibility that a passenger was involved.

Most of the 14 countries with passengers on the plane haven't disclosed how they conducted the background checks or what guidelines they followed in clearing passengers. Chinese officials didn't respond to requests for comment how it conducted its background checks on the 153 Chinese citizens on board. Malaysia, too, hasn't provided details other than to say it focused on possible terrorism, sabotage and personal or psychological issues.

Indonesia said it relied on international guidelines in clearing all of its seven passengers, but didn't say who wrote the guidelines. 'We don't use our own standard,' said police spokesman Agus Rikwanto. 'We use the standard used internationally that is used in investigating any suspicious individual. The results are they are cleared.'