Poland's new government on Thursday relaunched an inquiry into the death of President Lech Kaczynski in a plane crash in Russia in 2010, a move likely to strain Warsaw's relations with its former overlord, already fragile over the Ukraine crisis.
An inquiry by the previous government returned a verdict of pilot error but the winner of Poland's October election, the Law and Justice (PiS) party led by Kaczynski's twin brother Jaroslaw, says an onboard explosion could have caused the crash.
Speaking at a ceremony to announce the decision, Defense Minister Antoni Macierewicz also hinted at an explosion as a possible cause, saying the plane had "disintegrated" meters above the ground before crashing.
Though the PiS has never accused Russia of orchestrating the president's death it has said the Kremlin benefited from the crash, which also killed the central bank chief, top army brass and several lawmakers, triggering a period of political turmoil.
PiS officials have also accused Moscow of prolonging its own investigation and withholding evidence, including the black box flight recorders and wreckage from the plane.
Russia has kept the wreckage for nearly six years and says it cannot returned until its own criminal probe is concluded.