A passenger jet belonging to Russia's Saratov Airlines that vanished from the radar and crashed soon after takeoff from a Moscow airport killing all 71 occupants was fully intact until moment of impact, when the aircraft exploded and strewed wreckage across the snow-covered field into which it collided, Russian investigators in charge of the case said Monday.

A twin-engined Antonov AN-148 model belonging to the Saratov regional carrier departed Moscow's Domodedovo Airport on Sunday afternoon carrying 65 passengers and 6 crewmembers en route to the southern city of Orsk before it came down just 80 kilometers (50 miles) southeast outside the capital, near the village of Argunovo.

"It has been established that at the time of the crash the aircraft was intact," said the Investigative Committee of Russia in a statement. "An explosion occurred after the aircraft crashed," it added, saying also that two black boxes from the destroyed aircraft had since been located at the collision site.

The committee has launched a full-scale probe into the crash and has seized from the airline's offices aircraft maintenance documentation, crewmember medical records, air traffic control communication data, tracking files and fuel samples in a bid to cast some light onto what brought the aircraft down, the statement said.

Earlier, some 780 emergency service workers and soldiers began scouring the snowy spot where the jet crashed in an effort to recover debris and human remains, while a team of specialists was sent to Orsk, a city located to the south of the Ural mountain range, to carry out DNA tests on the relatives of the victims.

"The work at the scene is to be conducted around the clock. We plan on holding the main stage of the search operation here at the site of the incident over the course of seven days because we have a big area of scattered wreckage fragments," Russia's Emergency Situations Minister, Vladimir Puchkov, told reporters.

The regional emergencies minister for Moscow, Sergey Poletykin, told a press conference that around 200 fragments of human remains had been discovered so far.

A full list of all those who died in the crash was published by the emergencies ministry late Sunday, revealing that one child and two adolescents were among those killed.

The cause of the crash was not yet known.