The official, who spoke on condition of anonymity as he was not authorised to talk to the media, said Indonesian authorities said the plane did not show up on their military radar.
The plane could have deliberately flown around Indonesian airspace to avoid detection, or may have coincidentally travelled out of radar range, he said.
The revelation came as searchers for the missing Malaysia Airlines jet intensified in the southern Indian Ocean to determine whether a few brief sounds picked up by underwater equipment came from the plane's black boxes, whose battery-powered pingers are on the verge of dying out.
Meanwhile, Australia's Joint Agency Coordination Centre (JACC) said Monday that up to nine military planes, three civil planes and 14 ships will assist in search for missing Malaysia Airlines flight MH370.
The search area is expected to be approximately 234,000 sq km.
Royal Australian Navy's ship Ocean Shield is continuing investigations in its own area.
HMS Echo was en route to assist the Chinese vessel Haixun 01, which detected pulse signals in the Indian Ocean.
A Chinese ship picked up an electronic pulsing signal Friday and again Saturday, and an Australian ship carrying sophisticated deep-sea acoustic equipment detected a signal in a different area Sunday.
Malaysia Airlines flight MH370 vanished mysteriously about an hour after taking off from Kuala Lumpur shortly after midnight March 8.
The Boeing 777-200ER was scheduled to land in Beijing the same day. The 227 passengers on board included five Indians, 154 Chinese and 38 Malaysians.
Despite extensive scouring of the remote southern Indian Ocean area by planes and ships off the coast of Perth, where the plane is believed to have crashed, no trace has been found.