A US Navy "black box" detector made its much-anticipated debut in the oceanic hunt for flight MH370 on Friday but Australia's search chief warned it was crunch time with the box's signal set to expire soon.
As the extensive search wore on, Malaysian opposition leader Anwar Ibrahim said he believed the country's long-ruling regime was concealing information on the crisis, saying "the government knows more than us."
The Australian naval vessel Ocean Shield arrived with a "towed pinger locator" capable of homing in on signals from the black box, as 14 planes scoured the remote Indian Ocean search area for signs of a crash site.
The plane disappeared on March 8, and Australian authorities coordinating the search have rushed the pinger device into place before the black box's battery-powered location signal expires.
"On best advice, the locator beacon will last about a month before it ceases its transmissions, so we're now getting pretty close to the time when it might expire," said Angus Houston, head of a coordination centre directing the eight-nation search.
The plane went missing en route from Kuala Lumpur to Beijing with 239 people on board, confounding aviation experts and sparking criticism of Malaysian authorities who have been unable to explain how the jumbo jet vanished.
- Undersea search commences -
Anwar said he was "baffled" by the Malaysian military's failure to respond despite detecting the plane crossing back over the country's airspace following its mysterious detour.
"Unfortunately the manner in which this was handled after the first few days was clearly suspect," Anwar said in an interview with Britain's Daily Telegraph.
"One fact remains. Clearly information critical to our understanding is deemed missing. I believe the government knows more than us," he added, without elaborating.
Malaysian authorities say they still have no idea what caused the plane to veer off course, but believe that satellite data indicates MH370 crashed in the Indian Ocean, far off western Australia.
No debris has been found despite an extensive search. An approximate crash site needs to be determined for a black box search to be effective.
Houston said Ocean Shield, using the pinger locator, joined in an underwater search with the British navy's hydrographic ship HMS Echo, which on Thursday began scanning for black box transmissions.
"The Royal Australian Navy and Royal Navy have today commenced sub-surface search for emissions from the black box pinger from Malaysia Airlines flight MH370," he said.
The Ocean Shield also bore an underwater drone vehicle "for mapping the seafloor", authorities said.
Houston said planes and ships would continue looking for floating debris.
- Malaysia 'wasted time' -
Malaysia's government has a poor record on transparency, but Transport Minister Hishammuddin Hussein said this week it was "not hiding anything."
But Anwar, who recently had his acquittal on sodomy charges overturned in what he claims is a political smear by the government, said a "sophisticated" radar system that he authorised as finance minister in 1994 should have led to prompt military action.
Malaysia's armed forces said soon after the plane disappeared that military radar had picked up an unidentified object moving toward the Indian Ocean, but they did nothing because it was not deemed "hostile".
The decision has been criticised for losing valuable time in tracking MH370. It took Malaysia one week to confirm the radar blip was MH370, and to subsequently reorient a huge search away from its initial focus in the South China Sea.
Anwar said Malaysia should have moved quickly to save other countries scouring "a place that they know cannot be the site of the plane".
A Malaysian government spokesman said: "Anwar has made numerous unfounded allegations criticising Malaysia."
"Instead of trying to exploit the MH370 tragedy to score political points, it would be constructive if he could support the government as it coordinates the multinational search operation for MH370."
Malaysia's police chief Khalid Abu Bakar indicated this week an investigation of all 227 passengers and 12 crew into a possible hijack or sabotage plot had drawn a blank so far, adding soberly that authorities may never know what happened.
It is hoped that the cockpit voice recorder and flight data recorder, if recovered, can shed light on what happened.
Malaysia has faced impassioned accusations from distraught relatives of the 153 Chinese people on the plane, with many alleging a cover-up and calling Malaysian authorities "murderers."
China's government also has expressed its displeasure with Malaysia, and ties faced further strain over the kidnapping Wednesday of a Chinese tourist from a Malaysian diving resort by unidentified gunmen.