Malaysia said that a missing airliner had crashed into the Indian Ocean on Monday to the family and relatives of the passengers onboard who demand that Kuala Lumpur, from where the airliner originally took-off from, share all the evidence it had on the incident, according to the Associated Press.

Malaysian Prime Minister Najib Razak said that Malaysia Airlines Flight MH370, which vanished while flying to Beijing from Kuala Lumpur, had crashed thousands of miles away in the southern Indian Ocean, citing groundbreaking satellite-data analysis by the British company Inmarsat, the AP reported.

All 239 people on board were presumed dead, airline officials said on Monday, according to the AP.

Chinese Deputy Foreign Minister Xie Hangsheng immediately demanded all relevant satellite-data analysis from Malaysia that demonstrated how Malaysia had reached its conclusion about the fate of the jet, according to the AP.

Najib's announcement opens the way for what could be one of the most costly and challenging air crash investigations in history, the AP reported.

The launch of an official air crash investigation would give Malaysia power to coordinate and sift evidence, but it may still face critics, especially China, which had more than 150 citizens on board the missing plane and has criticised Malaysia over the progress of the search, according to the AP.

The Inmarsat data showed the Boeing 777's last position was in the Indian Ocean west of Perth, Australia, Najib said in a statement, the AP reported.

"This is a remote location, far from any possible landing sites," Najib said, according to the AP. "It is therefore, with deep sadness and regret, that I must inform you that, according to this new data, Flight MH370 ended in the southern Indian Ocean."

The U.S. Navy was flying in its high-tech black box detector to the area, the AP reported. The so-called black boxes, or the cockpit voice recorder and flight data recorder, record what happens on board planes during flight.

Flight MH370 vanished from civilian radar screens less than an hour after taking off from Kuala Lumpur on March 8, according to the AP. No confirmed sighting of the plane has been made since and there is no clue what went wrong.

Attention and resources in the search for the plane had shifted from an initial focus north of the Equator to an increasingly narrowed stretch of rough sea in the southern Indian Ocean, thousands of miles from the original flight path, the AP reported.

Investigators believe someone on the flight may have shut off the plane's communications systems, according to the AP. Partial military radar tracking showed it turning west and re-crossing the Malay Peninsula, apparently under the control of a skilled pilot.

That led them to focus on hijacking or sabotage, but investigators have not ruled out technical problems, the AP reported.