Officials previously have said that those words came at a point when one of the jetliner's data communications systems already had been switched off, and the timing has sharpened suspicions that one or both of the pilots may have been involved in the plane's disappearance. The detail would appear indicate that whoever spoke the words was deceiving ground control. However, it is not clear whether the system could have been turned off by one of the pilots - or someone else - without the other pilot's knowledge.

Malaysia's government in the meantime sent out diplomatic cables to all countries in the search area, seeking their help with the search, as well as to ask for any radar data that might help narrow the task. Some 26 countries are involved in the search, which initially focused on seas on either side of peninsular Malaysia, in the South China Sea and the Strait of Malacca.

Over the weekend, however, Malaysian Prime Minister Najib Razak announced that investigators determined that a satellite picked up a faint signal from the aircraft about 7 hours after takeoff. The signal indicated that the plane would have been somewhere on a vast arc stretching from Kazakhstan down to the southern reaches of the Indian Ocean.

Malaysian Defense Minister Hishammuddin Hussein announced Monday that searches in both the northern and southern stretches of the arc had begun, with countries from Australia up to Kazakhstan joining the hunt.

Had the plane gone northwest to Central Asia, it would have crossed over countries with busy airspace, and some experts believe the person in control of the aircraft would more likely have chosen to go south. However, authorities are not ruling out the northern corridor and are eager for radar data that might confirm or rule out that path.

The northern search corridor crosses through countries including China, India and Pakistan - all of which have indicated they have seen no sign of the plane so far.

An official with the Chinese civil aviation authority said the missing plane did not enter Chinese airspace, but the Chinese Defense Ministry and Foreign Ministry didn't immediately respond to questions on radar information.

Indonesian officials have said the plane did not cross their territory, based on radar data. Air force spokesman Rear Mar. Hadi Tjahjanto said Monday his country's search efforts were focusing on waters west of Sumatra in the Indian Ocean.

Australian Prime Minister Tony Abbott told parliament that he agreed to take the lead scouring the southern Indian Ocean for the ``ill-fated aircraft'' during a conversation Monday with Malaysia's leader.

"Australia will do its duty in this matter," Abbott told parliament. "We will do our duty to the families of the 230 people on that aircraft who are still absolutely devastated by their absence, and who are still profoundly, profoundly saddened by this as yet unfathomed mystery."

Australia already has had two AP-3C Orion aircraft involved in the search, one of them looking north and west of the remote Cocos Islands. The southern Indian Ocean is the world's third-deepest and one of the most remote stretches of water in the world, with little radar coverage.

Associated Press writers Chris Brummitt, Jim Gomez and Eileen Ng in Kuala Lumpur, Kirsten Gelineau in Sydney, Australia, Christopher Bodeen in Beijing and Niniek Karmini in Jakarta contributed to this report.