The first official Malaysian government report on the missing Malaysia Airlines plane notes a time-lag of more than four hours between the disappearance of Flight 370 from radar and the activation of a rescue operation.

The preliminary report, marked confidential, was released Thursday on the Facebook page of acting Malaysian Transport Minister Hishammuddin Hussein. It was conducted by the ministry's chief inspector of air accidents.

The report was made public as Malaysia Airlines called on the families of passengers of Flight 370 Thursday to return home to await word on their loved ones as the search for the missing plane enters a new phase.

Flight 370, with 239 people aboard, disappeared March 8 en route from Kuala Lumpur to Beijing.

The government report — only 23 paragraphs long — has also been sent to the International Civil Aviation Organization, the U.N. body for global aviation.

It notes that the plane disappeared from radar in Kuala Lumpur at 1:21 a.m. and should have checked in with air traffic control in Ho Chi Minh City, Vietnam. There is no indication that it did.

Yet it was 17 minutes before this anomaly was noted and more than four hours before an official rescue operation was mounted at 5:30 a.m. by the Kuala Lumpur Rescue Coordination Centre.

In the bare-bones language, the report says that Ho Chi Minh air traffic control "made a query" to Kuala Lumpur air traffic control at 1:38 a.m. "on the whereabouts of MH370." That triggered an attempt to establish contact.

"No contact had been established by any ATC units and thus the Rescue Coordination Centre (RCC) was activated at 5:30 a.m.," the report notes. It does not elaborate on the four-hour lag between these two events.

An intense search involving 20 countries, hundreds of ships, planes and experts, has failed to turn up even a shred of debris from the jet, which is believed to have crashed into the Indian Ocean. The airline notes that the international search effort will enter a "new phase" in the coming weeks.

The airline said in a statement on its website that the search will be a "prolonged process" and announced that on May 7 it will close assistance centers set up to help the next-of-kin and provide them with information in the aftermath of the tragedy. Most of the passengers were Chinese and the airlines has paid for their relatives to stay in hotels in Malaysia during the extensive search period.

MORE: Malaysia search shifts from surface to ocean floor

"Instead of staying in hotels, the families of MH370 are advised to receive information updates on the progress of the search and investigation and other support by Malaysia Airlines within the comfort of their own homes, with the support and care of their families and friends," the statement said.

Malaysia Airlines said that despite the intense search "we have to face the hard reality that there is still no trace of the aircraft, and the fate of the missing passengers and crew remains unknown till this day."

The airline said it was deeply sympathetic to the "continuing unimaginable anguish, distress and hardship" suffered by the families and pledged to stay in touch with them.

The airline also said it would make "advanced compensation payments" as soon as possible to family members "to meet their immediate economic needs."

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