A pilot aboard an Indonesian Air Force military surveillance aircraft flies over the Malacca Strait, a sea passageway between Indonesia and Malaysia, on March 13.(Photo: Indonesian Air Force)

KUALA LUMPUR, Malaysia — The search for missing Malaysia Airlines flight MH370 has expanded into the Indian Ocean as investigators focus on the theory that the jet may have flown well beyond the current search areas and possibly even for several hours after losing contact with airport authorities.

Six Indian navy and coast guard ships plus reconnaissance planes have searched eastern parts of Andaman seas over the past three days, and were expanding their search to areas west of the Andaman and Nicobar Islands chain Friday, said V.S.R. Murty, an Indian Coast Guard inspector.

Much of the early search has focused east of Malaysia in the South China Sea, where the aircraft last communicated with air traffic base stations about an hour after departing on a flight to Beijing.

On Thursday, the Wall Street Journal quoted U.S. investigators as saying they suspected the plane stayed in the air for about four hours after its last confirmed contact, citing engine data automatically transmitted to the ground as part of a routine maintenance program. The newspaper later corrected the account to say the information came from the plane's satellite communication link, not the engines.

A report published Friday by Reuters said that military radar-tracking evidence seen by investigators suggests an unidentified aircraft that those investigators believe is flight MH370 may have been deliberately flown toward the Andaman Islands. Reuters did not name the source of the information.

Kim Hjelmgaard reported from London. Contributing: Associated Press