Malaysian prime minister Najib Razak told a press conference in Kuala Lumpur that a new analysis by the UK Air Accidents Investigation Branch and tracking firm Inmarsat had revealed that MH370's last position was in the ocean west of Perth.
"This is a remote location, far from any possible landing sites," he said. "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."
He added that Malaysia Airlines had already spoken to the families of the passengers and crew to inform them of the latest development.
"For them the past few weeks have been heart-breaking. I know this news must be harder still," he said.
Mr Razak said a press conference would be held tomorrow with further details.