A U.S. official involved in the search for the missing Malaysian plane says the jet may have been flying four hours after it disappeared from radar screens.
The official said the jet was sending out a pinging signal -- a sign it was trying to communicate with a satellite. He said the plane may have flown another 4,000 kilometers after controllers reported it missing.
The United States is expanding its search for the plane into the Indian Ocean -- far west of its intended flight path.
Malaysia Airlines Flight 370 disappeared early Saturday during a flight from Kuala Lumpur to Beijing. Two-hundred-39 people were on board.
Aircraft and ships from 12 countries are looking for the Boeing 777, but so far have found nothing to clear up the mystery. Authorities have ruled nothing out, including a massive technical failure, terrorism or the possibility that the pilot wanted to commit suicide.