BartaBangla Desk :: The international search for the missing Malaysian jetliner expanded westward Friday toward the Indian Ocean amid signs the aircraft may have flown on for hours after its last contact with air-traffic control nearly a week ago.

A U.S. official told The Associated Press that the Malaysia Airlines plane sent signals to a satellite for four hours after the aircraft went missing early last Saturday, raising the possibility the jet carrying 239 people could have flown far from the current search areas. It also increased speculation that whatever happened to the plane was a deliberate act.

If the plane had disintegrated during flight or had suffered some other catastrophic failure, all signals — the pings to the satellite, the data messages and the transponder — would be expected to stop at the same time. Experts say a pilot or passengers with technical expertise may have switched off the transponder in the hope of flying undetected.

No theory, however, has been ruled out in one of aviation history’s most puzzling mysteries.

The Beijing-bound aircraft last communicated with air traffic base stations east of Malaysia in the South China Sea, which for several days has the main focus of the search. Planes and ships also have been searching the Strait of Malacca west of Malaysia because of a blip on military radar suggested the plane might have turned in that direction after the last confirmed contact.

If the plane flew another four hours, it could be much farther away.

Indian ships and planes have been searching northwest of Malaysia in the eastern Andaman Sea, and on Friday expanded their search to areas west of the Andaman and Nicobar Islands chain Friday, said V.S.R. Murty, an Indian Coast Guard inspector-general.

The White House said the U.S. may be drawn into a new phase of the search in the vast Indian Ocean but did not offer details. The U.S. Navy 7th Fleet said it was moving one of its ships, the USS Kidd, into the Strait of Malacca.

Vietnam, which has been heavily involved in the search from the start, downgraded its hunt in the South China Sea to regular from emergency by reducing the frequency of aircraft flights and cruises by ships involved, said Lt. Gen. Vo Van Tuan, deputy chief of staff of Vietnamese People’s Army.