Malaysia said Monday the search for a missing passenger jet is under way along both the northern and southern corridors where it is believed to have been deliberately diverted.
Defense Minister Hishammuddin Hussein says 26 countries are now involved in the search, including in water, and on land in 11 countries. The search spans tens of millions of square kilometers.
Investigators believe the Boeing 777 flew either north toward Central Asia or south deeper into the vast Indian Ocean in the hours after it mysteriously vanished on March 8.
Australia on Monday agreed to take charge of the southern section of the search, at the request of Malaysian Prime Minister Najib Razak.
"He asked that Australia take responsibility for the search in the southern vector, which the Malaysian authorities now think was one possible flight path for this ill-fated aircraft. I agreed that we would do so. I offered the Malaysian prime minister additional maritime surveillance resources which he gratefully accepted."
Earlier, Mr. Abbott said he had not seen any signs the Malaysia Airlines flight carrying 239 people had come close to Australian airspace.
Meanwhile, Malaysian investigators are more closely examining the final moments before the plane disappeared from civilian radar.
Malaysia Airlines CEO Ahmad Jauhari Yahya says the last known message from the cockpit - a calm, "All right, goodnight" - is believed to have come from the plane's co-pilot.
But investigators now say it is not clear whether the radio transmission came before or after a signaling system was partially disabled or switched off, allowing the plane to further avoid detection.
The voice in the cockpit did not mention any trouble on board, suggesting he may have been misleading ground control or acting under coercion by someone familiar with aviation technology.
Family members of those missing and countries involved in the search have criticized Malaysia for repeatedly releasing seemingly contradictory or incomplete information.
China's Foreign Ministry Monday urged Malaysia to "immediately" expand and clarify the scope of the search, saying it should provide "more thorough, accurate information to countries participating."
Defense Minister Hishammuddin Monday denied holding back crucial information. He said he would not withhold any details that could help, but that any information released "must be verified by international investigation teams."
Authorities are also increasing their scrutiny of the pilots, searching their homes in the quest for clues. Police are examining an elaborate flight simulator taken from one of them. Authorities also are questioning engineers who may have had contact with the plane before it left Kuala Lumpur.
A full-scale criminal investigation was triggered when Malaysian Prime Minister Najib said Saturday there is a "high degree of certainty" that someone who knew what he was doing deliberately turned off the jet's communications systems.
Investigators say the plane had enough fuel to fly for several hours after disappearing from radar.
Authorities also have not ruled out the possibility the plane was on the ground at an unknown location when some satellite signals were sent.
The missing passenger plane was flying from Kuala Lumpur to Beijing when it disappeared. About two-thirds of the people on board were Chinese. Other passengers included Europeans and Americans.