(CNN) -- More than four days since Malaysia Airlines Flight 370 disappeared over Southeast Asia, Malaysian officials not only don't know what happened to the plane, they don't seem sure where to look.
On Wednesday, officials announced they have once again expanded the search area. It now covers 27,000 square miles -- in the Straits of Malacca and in the South China Sea.
The lack of a clear direction prompted Vietnam to say Wednesday that it's pulling back on its search efforts until Malaysian authorities come up with better information on where to look.
"We have scaled down the searches for today and are still waiting for the response from Malaysian authorities," Phan Quy Tieu, Vietnam's vice minister of transportation, told reporters.
He described as "insufficient" the information provided so far on the airline, which vanished early Saturday over Southeast Asia with 239 people on board.
At a news conference Wednesday, Malaysian transportation minister Hishamuddin Bin Hussein defended his government's approach.
"We have been very consistent in the search," he said.
The path of the plane
Part of the cause of the veiled irritation on the Vietnamese side seems to concern the deepening mystery over the path the plane may have taken after it lost contact with air traffic control on its scheduled flight from Kuala Lumpur to Beijing.
A senior Malaysian air force official on Tuesday told CNN that after the plane lost all communications around 1:30 a.m. Saturday, it still showed up on radar for more than an hour longer. Before it vanished altogether, the plane apparently turned away from its intended destination and traveled hundreds of miles off course, the official said.
It was last detected, according to the official, near Pulau Perak, a very small island in the Straits of Malacca, the body of water between the Malay Peninsula and the Indonesian island of Sumatra.
Those assertions, reported by CNN and other new organizations, have fueled surprise among aviation analysts and a fresh burst of theories about what might have happened to the plane. They also appear to have created tensions between some of the different countries involved in the search efforts.
Uncertainty over exact path
But some Malaysian officials have reportedly cast doubt on the details of the change in direction.
The New York Times cited Tengku Sariffuddin Tengku Ahmad, spokesman for the Prime Minister's office, as saying that he had checked with senior military officials, who told him there was no evidence that the plane had flown back over the Malay Peninsula to the Straits of Malacca, only that it may have attempted to turn back.
The Prime Minister's office didn't immediately return calls from CNN seeking comment Wednesday.
But the air force chief Gen. Rodzali Daud didn't go as far as denying that the plane had traveled hundreds of miles off course.
The air force is still "examining and analyzing all possibilities as regards to the airliner's flight paths subsequent to its disappearance," he said in a statement Wednesday.
Rodzali said it "would not be appropriate" for the air force to "issue any official conclusions as to the aircraft's flight path until a high amount of certainty and verification is achieved."
He denied, though, that he had made statements to a Malaysian newspaper similar to those that the senior air force official made to CNN.
Searchers find no trace
The reported change of course would fit in with some of the areas that search and rescue teams have been combing over the past several days.
Forty-two ships and 39 planes from 12 countries have been searching the sea between the northeast coast of Malaysia and southwest Vietnam, the area where the plane lost contact with air traffic controllers.
But they are also looking off the west coast of the Malay Peninsula, in the Straits of Malacca, and north into the Andaman Sea -- areas that would tally with a change of direction by the plane.
They are also searching the land surface in between those areas.
So far, though, searchers have found no confirmed trace of the plane anywhere.
Vietnam scales back searches
Vietnamese authorities, who have been heavily involved in the search, appeared to be showing increasing frustration Wednesday with the information coming from the Malaysian side.
"Up until now we only had one meeting with a Malaysian military attache," Phan, the vice transportation minister, said. "However, the information they have provided is insufficient."
Vietnam informed Malaysian authorities that the plane was turning westward at the time it disappeared but didn't hear anything back, Phan said.
For the moment, Vietnamese teams will stop searching the sea south of Ca Mau province, the southern tip of Vietnam, and shift the focus to areas east of Ca Mau, said Doan Luu, the director of international affairs at the Vietnamese Civil Aviation Authority.
Doan also told CNN that Vietnam has asked Malaysian authorities to clarify which location is the focus of their search, but that it has yet to hear back.
Families' frustration
Families of those on board the plane also want to know more, and some have vented their anger.
"Time is passing by, the priority should be to search for the living!" a middle-aged man shouted at meeting with airline officials in Beijing on Tuesday before breaking into sobs. His son, he said, was one of the passengers aboard the plane.
Other people at the meeting also voiced their frustration at the lack of information.
Most of those on the flight were Chinese. And for their family members, the wait has been long and anguished.
Malaysian Prime Minister Najib Razak on Wednesday appealed to families of the people on board to be patient.
"What we want to tell them is that we must, indeed, consider their feelings," Najib said. "The families involved have to understand that this is something unexpected. The families must understand more efforts have been made with all our capabilities."
The Chinese government had on Monday urged Malaysia to speed up the investigation into what happened to the plane.
Analysts puzzled
The possibility that the plane changed direction and flew over the Straits of Malacca has perplexed aviation experts.
Peter Goelz, former managing director of the National Transportation Safety Board, said he thinks the information, if correct, ominously suggests that someone purposefully cut off the transponder -- which sends data on altitude, direction and speed -- and steered the plane from its intended destination.
"This kind of deviation in course is simply inexplicable," Goelz said.
Other experts aren't convinced that there was necessarily foul play involved. They say there could have been some sort of sudden catastrophic electronic failure that spurred the crew to try to turn around, with no luck.
"Perhaps there was a power problem," said veteran pilot Kit Darby, former president of Aviation Information Resources, adding that backup power systems would only last about an hour. "(It is) natural for the pilot, in my view, to return to where he knows the airports."
Still, while they have theories, even those who have piloted massive commercial airliners like this one admit that they can't conclude anything until the plane is found.
Authorities have said they're not so far ruling out any possibilities in their investigations.
For now, the massive multinational search has yielded no breakthrough -- which has only added to the heartache for the friends and family of the 239 passengers and crew on board.
CNN's Khushbu Shah, Michael Pearson, Kathy Quiano, Sarita Harilela, David Molko and Pauline Chiou, and journalist Ivy Sam contributed to this report.
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