China, where the bulk of the passengers were from, expressed irritation over what it described as Malaysia's foot-dragging in releasing information about the search.
Investigators now have a high degree of certainty that one of the plane's communications systems -- the Aircraft and Communications Addressing and Reporting System -- was disabled before the aircraft reached the east coast of Malaysia, Najib said. Shortly afterward, someone on board switched off the aircraft's transponder, which communicates with civilian air traffic controllers.
Najib confirmed that Malaysian air force defense radar picked up traces of the plane turning back westward, crossing over Peninsular Malaysia into the northern stretches of the Strait of Malacca. Authorities previously had said this radar data could not be verified.
"These movements are consistent with deliberate action by someone on the plane," Najib said.
