A Polish government commission says a plane carrying Poland’s president may have disintegrated due to an explosion shortly before it crashed in western Russia in 2010, killing all people on board.

The preliminary finding from a government-appointed commission was released on April 10, the 7th anniversary of the crash near the Russian city of Smolensk that killed President Lech Kaczynski and 95 others.

The delegation, which included Kaczynski’s wife, Poland’s top military leadership, and the governor of Poland’s central bank, was traveling to Russia to commemorate thousands Polish officers who were executed in the Katyn Forest by Soviet secret police in 1940.

An investigation by Poland's previous, centrist government ruled that the crash of the government’s Soviet-made TU-154 airplane in heavy fog during an attempt to land was the result of pilot error.

But Kaczynski’s twin brother, Jaroslaw, has said an onboard explosion could have caused the crash. The ruling party that he leads, Law and Justice, launched a fresh probe into the incident.

The commission now investigating the crash was created by Defense Minister Antoni Macierewicz, who last month accused Poland’s former President Donald Tusk, who is the current European Council president, of committing "diplomatic treason" in connection with the earlier probe.

The accusations have been dismissed as ridiculous by both Tusk and Russia.

"Much indicates that on April 10, 2010, an explosion took place on board the government Tupolev plane," said the commentary accompanying a video released by the commission on April 10.

"As a result of the conducted experiments, we can say that the most likely cause of the explosion was a thermobaric charge initiating a strong shockwave," it added.

Waclaw Berczynski, who leads a team of Polish investigators, told public broadcaster TVP Info on April 10 that the TU-154 "started to break up and lose parts in the air” and that the tree that the plane clipped with its wing "had no impact on the crash."

The commission also repeated allegations made by Polish prosecutors last week that Russian air traffic controllers had “deliberately” directed the plane to the incorrect descent path. The prosecutors said they would press charges against the two air-traffic controllers, while Russia rejected those charges.

The claims by the commission are likely to heighten tensions between Warsaw and Moscow, which has rebuffed Polish requests to return the plane’s wreckage.

Russia says it will do so only after it has completed its own inquiry into the crash.

With reporting by Reuters, AP, and AFP