Malaysia Airlines sent a text message to Flight 370 before relatives were briefed at hotels according to airline spokeswoman Adlina Azharuddin.
The text message read: "Malaysia Airlines deeply regrets that we have to assume beyond any reasonable doubt that MH370 has been lost and that none of those on board survived. As you will hear in the next hour from Malaysia's Prime Minster we must now accept all evidence suggests the plane went down in the Southern Indian Ocean."
Malaysia Airlines is "working on an arrangement" to fly families of Flight 370 passengers to Australia once wreckage is found, an airline representative said Monday.
The announcement came the same day as Australian officials said they had spotted two objects in the southern Indian Ocean that could be related to the flight, which has been missing since March 8 with 239 people aboard.
One object is "a grey or green circular object," and the other is "an orange rectangular object," the Australian Maritime Safety Authority said.
The objects are the latest in a series of sightings, including "suspicious objects" reported earlier Monday by a Chinese military plane that was involved in search efforts in the same region, authorities said.
So far, nothing has been definitively linked to Flight 370.