Kaczyński's right-wing Law and Justice party (PiS; affiliated to the European Parliament's conservative ECR group), known for its deep distrust of Russia, presented its report into the causes of the plane crash which killed all 96 on board including President Lech Kaczyński and his wife Maria in Smolensk, western Russia.
An earlier Russian probe put the blame solely on the Polish side, but Poland has argued that Russian ground controllers in Smolensk also inadvertently contributed to the crash, which happened while the plane was trying to land in thick fog.
"Given the weather conditions, the Russians should have closed the airport. The Polish pilots were knowingly led to their death," said Antoni Macierewicz, the main author of the report.
"A dramatic conversation between ground controllers and their headquarters, where they [the controllers] begged for a backup airport to be granted, shows that. But their HQ refused and ordered them to land the plane," he told a news conference.
The report said Russia failed to deliver a compulsory weather forecast to the Poles and had unlawfully withdrawn all security officers designated to protect Kaczyński from the airport. It also accused Moscow of forging or hiding many documents crucial for the investigation.
"The key conclusion is that the main burden of guilt for what happened lies with the Russians, though some share of the guilt, related to the procedures after the crash, also lies on the Polish side," Kaczyński told the news conference.
Poland holds national elections in October and Tusk's ruling centrist Civic Platform is on track to win a second four-year term. Kaczyński's PiS is expected to come in second place.
Last year's crash caused an outpouring of grief and compassion among Russians, reinforcing a cautious economic and political rapprochement launched previously by Tusk and Russia's Prime Minister Vladimir Putin.
But Russia's handling of the investigation and its final report irked Warsaw and Tusk's low-key approach to the issue - branded treasonable by Kaczyński - may become a key theme of the election campaign.
EurActiv with Reuters