MH370 The communication systems of Malaysia Airlines Flight MH370 that disappeared from civilian radar last Saturday may have been deliberately turned off, according to reports citing US investigators.

US officials believe the flight's two communication systems were "systematically shut down", indicating that the plane's disappearance may not have been due to a catastrophic failure, according to ABC News .

"The data reporting system, they believe, was shut down at 1.07am. The transponder - which transmits location and altitude - shut down at 1.21am," the report says.

Meanwhile, Washington Post similarly quoted US sources as saying that somebody in the cockpit may have turned off the transponder on purpose, before flying on.

“The fact that a modern airplane with a huge amount of redundancy appeared to change course at the same time that the transponder was turned off, that suggests that someone unauthorised took control of that airplane, like an intruder or one of the pilots,” a US air crash expert is quoted as saying.

Despite Malaysian authorities insisting the flight was undetectable after communication systems went inactive after the said time, a Wall Street Journal report said US investigators believe the Boeing 777 flew for a total of four hours.

The report said this was based on data automatically downloaded and sent to the ground from its engines as part of a standard monitoring programme called "Aircraft Communications Addressing and Reporting System (Acars)".

Later that day, MAS chief executive officer Ahmad Jauhari Yahya denied the claim.

"Based on our records, the last Acars (Aircraft Communications Addressing and Reporting System) transmission was done at 1.07am local time, and that was the last transmission (of engine data) that we have received from the aircraft. It did not run beyond that," he had said.

'Transport Ministry will not speculate'

It was later clarified that signals from the plane were not from the Acars system but 'pings' from the aircraft maintenance troubleshooting system attempting establish satellite contact.

However, the pings alone are not proof that the plane was in the air or on the ground but merely that it is still capable of communicating, sources were quoted as saying by Reuters .

Following the latest clarification, the Malaysian Transport Ministry declined to speculate whether the aircraft had indeed continue flying for several hours.

"As is standard procedure, the investigation team will not publicly release information until it has been properly verified and corroborated.

"Any new evidence should be passed to the investigation team in Malaysia in order to assist the investigation," the ministry said in a statement this afternoon.

Flight MH370 disappeared from civilian radar on March 8 over the Gulf of Thailand after taking off from Kuala Lumpur at 12:40am and was due to arrive in Beijing at 6.30am.

The Royal Malaysian Air Force (RMAF) said military radar picked up an unidentified aircraft in the Malacca Straits at 2.15am, but is unsure if it is the missing MH370.

Malaysia Airlines had said that the flight had enough fuel to fly until 8.30am that day.

These information have led US officials to study the possibility that the plane may have flown into the Indian Ocean, almost a week after fruitless searches in the South China Sea, Gulf of Thailand and Malacca Straits.

The USS Kidd is already en route to waters between the Indian Ocean and Andaman Sea to investigate this theory.