Poland is marking the fifth anniversary of the 2010 plane crash in Russia that killed its president, Lech Kaczynski, and 95 others.
The investigation into the crash is still going on.
This week a Polish radio station, RMF FM, leaked a transcript of cockpit recordings suggesting that presidential aides had put pressure on the pilots to land at Smolensk despite thick fog.
Polish military prosecutors called the transcript “imprecise”.
The plane wreckage remains in Russia.
The disaster happened as the president, his wife and top government officials were travelling to Katyn, the remote wooded spot where Soviet secret police murdered thousands of Polish officers in 1940.
The Russian-built Tupolev Tu-154 airliner crashed just short of the runway near Smolensk in western Russia, after it hit trees in heavy fog.
The BBC’s Adam Easton in Warsaw writes:
The plane crash that killed so many state and military leaders initially united the country in mourning – such was magnitude of the tragedy. But within weeks the solidarity had disappeared and the divisions remain to this day.
The political camp that suffered most losses in the disaster is now the country’s main opposition party – conservative Law and Justice (PiS), led by Lech Kaczynski’s identical twin brother Jaroslaw. It has boycotted the official commemoration for the last four years.
The terrible tragedy has been abused as a political tool. So far all official investigations have concluded the crash was mainly caused by poorly trained pilots attempting to land in dense fog at Smolensk military airfield. They have ruled out sinister plots.
This week’s revelations have added weight to what many suspected – that the pilots felt pressure to make the landing attempt, in order to be on time for the Katyn massacre commemoration.
However, Mr Kaczynski’s camp has encouraged people to believe it was not an accident, but an assassination concocted by the Russians and Lech Kaczynski’s political foes. One in five Poles agree with him, according to a survey this week conducted for the daily Gazeta Wyborcza.
The official ceremony took place at the Powazki military cemetery, where President Bronislaw Komorowski laid a wreath at a memorial plaque.
But a large crowd held Polish flags aloft outside the presidential palace in Warsaw, where the Law and Justice (PiS) party – previously led by Lech Kaczynski – held its own commemoration ceremony.
According to the leaked transcript, Polish air force commander-in-chief Andrzej Blasik was in the cockpit and told the pilots just before the crash: “You’ll make it easily”.
The transcript suggests that the pilots were distracted by people in or around the cockpit in the crucial minutes when they were deciding whether or not to land.
RMF FM radio said Polish investigators had used new techniques to decipher parts of the cockpit voice recording, provided by the Russian authorities. The poor quality of the recording has hampered the investigation.