Thousands of Polish nationalists rallied in Warsaw on Wednesday, three years after ex-president Lech Kaczynski died in a jet crash in Russia that they insist was an assassination.
They cheered on Kaczynski's twin brother Jaroslaw -- who heads the conservative Law and Justice (PiS) party -- when he questioned whether the crash at the Smolensk airport was indeed an accident.
"This tragedy has not been forgotten. We have a right to demand the truth," the 63-year-old said at the presidential palace, where he earlier laid flowers and sang the national anthem.
"Poland has millions of patriots who will not let themselves be manipulated," he said.
His supporters flew the red-white national flag and carried signs hostile to his arch-rival, Prime Minister Donald Tusk: "Smolensk, a crime by Tusk's crew".
PiS has repeatedly accused Tusk's centre-right government of not taking Russia to task over what it insists was a botched investigation and cover-up.
Both Polish and Russian investigators concluded the April 10, 2010 disaster that killed 96 people -- scores of them senior statesmen -- was an accident.
Their Russian-made Tu-154 airliner went down in thick fog while approaching Smolensk airport in western Russia.
The delegation was en route to memorial ceremonies in Katyn for thousands of Polish army officers slain by the Soviet secret police in 1940, a massacre the Kremlin denied until 1990.
In a new report published Wednesday, a parliamentary group led by PiS legislator Antoni Macierewicz highlighted its "conviction that the catastrophe followed explosions".
The analysis ignores Polish prosecutors' conclusion that no explosive traces were found on the wreck of the jet.
"It turns out that... Russian intelligence services decided which firms and when Poland's most important planes would be overhauled," Macierewicz said in the report, quoted by the Polish press agency PAP.
According to a survey published last month, a third of Poles said they "would not exclude" the possibility of an assassination.
On Wednesday, Tusk knelt before the graves of around 30 of the crash victims at the capital's Powazki Cemetery, while a government delegation visited the accident site and Warsaw held several memorials.
Lech Kaczynski's daughter laid flowers at Wawel Castle in Krakow, where her father and mother Maria, who also died in the crash, are buried.
"My pain is as fresh as it was three years ago," Marta Kaczynska told reporters.
Around 300 supporters of Polish nationalist groups rallied late Tuesday at the Russian embassy in Warsaw, accusing Russian and Polish leaders of having a hand in the crash.
They also called on Moscow to stop foot-dragging and hand over the plane's wreckage to Poland.
"It was not an accident. I understood that from the moment I turned on the TV. They're telling us nonsense," Warsaw resident Wieslaw Zukowski told AFP.
"In Russia, nothing happens by accident," he added.
In an August report, Polish investigators said most of the blame for the crash lay with Poland but also faulted Russia for the sub-standard Smolensk airfield and poor traffic control.
But it ruled out "extremist versions" of events, including sabotage and third-party pressure on the crew to land despite bad weather.
However, a Russian probe from 2011 concluded that the crew was under "psychological pressure" to land in very poor visibility.