The government commission set up by Defence Minister Antoni Macierewicz also claimed that Russian air traffic controllers deliberately misled Polish pilots about their location as the presidential plane was approaching the runway of the Smolensk military airport in 2010.
“The last phase of the tragedy was caused by an explosion which took place in the hull, and which destroyed the plane, breaking it up into fragments and tens of thousands of shards, at the same time killing the passengers,” said a commentary accompanying a video presentation outlining the work of the commission so far.
The Tupolev plane carrying President Lech Kaczyński and 95 others crashed on 10 April 2010. All aboard were killed. The victims included First Lady Maria Kaczyńska and dozens of senior Polish government officials and military commanders.
The presentation on Monday said: "As a result of experiments, we can say that the most likely cause of the explosion was a thermobaric charge initiating a strong shockwave, which destroyed obstacles encountered, ruptured the hull of the aircraft, threw out seats and the bodies of the victims, and ripped off their clothes. Is this what happened in Smolensk on 10 April, 2010?"
Parts of the left wing began to fall to the ground about 900 metres before the start of the runway, the report added.
A new commission to investigate the crash was set up by the governing Law and Justice (PiS) party which came to power in 2015.
The party is headed by Jarosław Kaczyński, twin brother of Poland’s late President Lech Kaczyński.
PiS has long challenged an official report into the crash issued by the previous Polish government which cited a catalogue of errors on the Polish side, while also pointing to errors made by Russian staff at the control tower of Smolensk Military Airport.
A Russian report placed all the blame on the Poles.
Despite repeated requests from Warsaw, Russia has refused to return the wreckage of the plane back to Poland.
Events around Poland on Monday marked the seventh anniversary of the disaster.
The presentation suggested that Polish pilots had been misled, adding that other aircraft landing on April 10 at the Smolensk airport before the Polish presidential plane were guided in according to procedures.
But the Polish plane was forced to take a sharper descent and 100 meters above the landing strip, instead of an expected command to land or to circle the airport again, the Polish aircraft was met with silence, according to the presentation.
"Failures recorded in the last seconds of the flight, a total loss of power prior to first contact with the ground, the location of remains of the wreckage, the specific nature of body injuries, aerodynamic tests, the force with which doors were driven into the ground. These and many other factors dictated to the [commission] to treat the possibility of an explosion as quite real,” the presentation added.