KUALA LUMPUR, Malaysia -- Some 26 countries are now involved in the massive international search for Malaysia Airlines Flight 370, authorities said Monday.

The unprecedented hunt is taking place as preliminary investigations revealed that the plane's co-pilot may have spoken the last words to air-traffic controllers.

Malaysia Airlines CEO Ahmad Jauhari Yahya said at a news conference that initial indications are that the co-pilot of the missing jetliner is the one who calmly said, All right, good night.

Officials previously have said that those words came at a point in the March 8 flight when one of the jetliner's data communications systems already had been switched off.

The timing of the last words has sharpened suspicions that one or both of the pilots may have been involved in the plane's disappearance.

The development comes as the search-and-rescue mission has been extended to what officials are calling two corridors that the plane may have flown from its last known position. One is an arc north toward central Asia, the other is an arc south toward the southern Indian Ocean and Australia.

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 227 passengers and 12 crewmembers) on that aircraft who are still absolutely devastated by their absence, and who are still profoundly, profoundly saddened by this as yet unfathomed mystery.

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