Adding another puzzling twist to the MH370 saga, US investigators now suspect that based on engine data, the plane remained airborne long after radar disappearance.

A Wall Street Journal report said investigators believe that the Boeing 777 with 239 people on board had flown for about four hours or hundreds of miles past the time it reached its last confirmed location.

However, at 5.30pm today, the Malaysian authorities have denied the contents of the report, stating that the last engine data transmission happened at 1.07am, stressing that this data has been scrutinised by the airplane manufacturer.

Quoting those familiar with the investigation, the WSJ report said the information was obtained from the data automatically downloaded and sent to the ground from the Boeing 777's engines as part of a routine maintenance and monitoring programme.

The financial daily also said that counter-terrorism officials are probing the possibility of the pilot or someone else had diverted the aircraft towards an undisclosed location after turning off the jetliner's transponders to avoid radar detection.

The report comes as authorities remain uncertain about which ocean to search for the jetliner that went missing on Saturday after taking off from Kuala Lumpur.

The last definitive sighting of the aircraft on civilian radar screens came shortly before 1.30am on Saturday, less than an hour after taking off from Kuala Lumpur, as it flew northeast across the mouth of the Gulf of Thailand bound for Beijing.

Describing the investigation as fluid, WSJ added that it is not clear if investigators had evidence indicating possible terrorism or espionage.

"So far, US national security officials have said that nothing specifically points toward terrorism, though they haven't ruled it out.

"But the huge uncertainty about where the plane was headed, and why it apparently continued flying so long without working transponders, has raised theories among investigators that the aircraft may have been commandeered for a reason that appears unclear to US authorities.

"Some of those theories have been laid out to national security officials and senior personnel from various US agencies, according to one person familiar with the matter ," read the report.

At one briefing, WSJ said officials were told that investigators are actively pursuing the notion that the plane was diverted "with the intention of using it later for another purpose".

A total flight time of five hours, including the one hour it was airborne before losing contact, could see the jet reaching as the Indian Ocean, the border of Pakistan or even the Arabian Sea.

According to WSJ , the engines' onboard monitoring system is provided by their manufacturer, Rolls-Royce PLC, and it periodically sends data about engine health, operations and aircraft movements to facilities on the ground.

"As part of its maintenance agreements, Malaysia Airlines transmits its engine data live to Rolls-Royce for analysis.

"The system compiles data from inside the 777's two Trent 800 engines and transmits snapshots of performance, as well as the altitude and speed of the jet.

"Those snippets are compiled and transmitted in 30-minute increments, said one person familiar with the system."

No such data exists

Meanwhile, a senior Malaysia Airlines official told Reuters that no such data existed, while a second official said he was unaware of it.

A spokeswoman for engine manufacturer Rolls-Royce had no immediate comment.

Malaysia Airlines has said previously that the Trent engines stopped transmitting monitoring signals when contact with the plane was lost.

As frustration mounts over the failure to find any trace of the plane, China heaped pressure on Malaysia to improve coordination in the search. Around two-thirds of the people aboard the lost plane were Chinese.

Vietnamese and Malaysian planes scanned waters where a Chinese government agency website said a satellite had photographed three "suspicious floating objects" on Sunday.

The location was close to where the plane lost contact with air traffic control.

Aircraft repeatedly circled the area over the South China Sea but were unable to detect any objects, said a Reuters journalist aboard one of the planes.

One US official close to the investigation said the Chinese satellite report was a "red herring".

Yesterday, Malaysia's air force chief said military radar had traced what could have been the jetliner to an area south of the Thai holiday island of Phuket, hundreds of miles to the west of its last known position.

His statement followed a series of conflicting accounts of the flight path of the plane, which left authorities uncertain even which sea to search.

In a related development, India's Defence Ministry ordered the deployment of ships, aircraft and helicopters from the remote Andaman and Nicobar Islands today to search for a missing Malaysian airliner that disappeared from radar screens last Saturday.