KUALA LUMPUR/PARIS (Reuters) - Malaysia on Thursday released its most comprehensive account yet of what happened to missing Flight MH370, in a preliminary report that detailed the route the plane probably took as it veered off course and revealed the confusion that followed.

It showed four hours elapsed between the first sign that the Malaysia Airlines jet had failed to report in when expected to and the decision to mount a search operation - and that time included lapses of communication and a false lead from the airline itself.

The document, dated April 9, also contributed to a growing safety debate by urging the International Civil Aviation Organization (ICAO), the U.N. body that oversees aviation, to consider introducing a system for tracking commercial jets.

The call comes ahead of a meeting at the Montreal-based agency later this month to address mounting pressure for improvements to fill communications blind spots over the world's oceans, but until now regulators have said such systems still need to be proven despite lobbying by the satellite industry.

The Malaysian government and military have come under intense criticism for their handling of events on and after March 8, when the Malaysia Airlines flight from Kuala Lumpur to Beijing disappeared with 239 passengers and crew on board.

Although the preliminary report issued by the Ministry of Transport leaves many key questions about what happened nearly eight weeks ago unanswered, and is not intended to resolve speculation about the cause, Malaysia may be hoping it sets the record straight on at least some of the contentious issues.

The fate of Flight MH370 remains a mystery despite the biggest search operation in commercial aviation history, and relatives of the passengers on board are desperate for confirmation of what happened to their loved ones.

Boeing, the manufacturer of the 777 aircraft, will also be keen to learn exactly what caused the plane to veer sharply off course and disappear from sight, and in particular whether it was mechanical failure or human intervention.

While not ruling out technical faults, a parallel Malaysian police investigation has so far focused on the pilots amid signs that the aircraft followed a twisting and deliberate course for at least the first hour of its journey off course.

THAILAND AND INDONESIA

The report confirmed that military radar tracked a plane as it turned in a westerly direction across the Malaysian Peninsula on the morning of March 8, and said the radar operator took no further action because the aircraft was deemed "friendly".

In an accompanying statement, Defence and Acting Transport Minister Hishammuddin Hussein said the military data was played back that morning and after he and Prime Minister Najib Razak were informed of the possible turnback, military ships and an aircraft were sent to look for MH370 in the Straits of Malacca.

The report also described what appeared to be frantic attempts to trace the aircraft, with air traffic control in Kuala Lumpur contacting counterparts in Singapore, Hong Kong and Phnom Penh, Cambodia, when something appeared to have gone awry.

Kuala Lumpur was initially informed of a problem when air traffic controllers in Ho Chi Minh City, Vietnam, who were meant to take over monitoring MH370 around the time the plane disappeared, said they had not heard from its pilots.

They told their Malaysian counterparts the "radar blip" had disappeared at a navigation point called BITOD about half way between Malaysia and Vietnam. Investigators suspect the aircraft's radar transponder was turned off at about that time.

The airline at first wrongly told controllers the jet was over Cambodia and later that it had passed over Vietnam, but this turned out to be a projection rather than real information.

Released to the public for the first time were recordings of conversations between the cockpit of MH370 and Kuala Lumpur air traffic control and maps showing MH370's probable flight path.

The pilot recordings, ending with a deadpan "good night" and the call sign, begin with the first contact on the ground and appear business-like, without any obvious signs of stress.

According to the maps, MH370 turned back from the South China Sea, cut across the southernmost tip of Thailand near the border with the Malaysian state of Kelantan and then flew across the Malaysian Peninsula.

It made a turn to the west in the Straits of Malacca near Penang and flew beyond the limits of Malaysian military radar.

ELECTRONIC HANDSHAKES

From this point, investigators have had to rely on an estimated course based on electronic handshakes picked up by a UK satellite, which came to light days after the disappearance.

After leaving Malaysian military radar coverage, investigators believe MH370 turned south and flew over the northern tip of Indonesia's Sumatra Island before heading for the southern reaches of the Indian Ocean off Australia's western coast, where a massive underwater search is now concentrated.

The course, contradicting reports the plane skirted round Indonesian airspace, raises potentially awkward questions over why Indonesia did not identify the aircraft on its own radar. Sensitivities over the sharing of data have been a recurring theme in the search for the jet, according to people involved.

The report identified three areas in the southern Indian Ocean where they can say with different levels of certainty that the jet crashed, but although searchers identified pings from its black boxes a thorough seabed search has been fruitless.

Australian Prime Minister Tony Abbott has said that the seabed search over a wider area could take 6-8 months, but some experts say it could take even longer, possibly years.

Fuelling the debate over tracking, Malaysia's Transport Ministry pointed to the disappearance of Flight MH370 and Air France Flight AF447 in 2009 as evidence that a system for real-time tracking would help to locate missing aircraft more easily.

Details of the initial findings including the audio tapes were shared before the report's publication with mainly Chinese relatives who have protested about Malaysia Airlines' handling of the case, in particular the use of text messages to inform some relatives when the aircraft was deemed to have crashed.

The airline urged families who have remained in Kuala Lumpur to return home, saying they would be kept informed, and pledged to pay early compensation to those who qualified. Such payments would not affect their rights to claim additional compensation.

Thailand