Poland’s ruling nationalists held scaled-down events to commemorate the 10th anniversary of a plane crash in Russia that killed top politicians and military officers, and renewed criticism of Moscow’s handling of the disaster.

Senior officials laid wreaths on Friday at a monument in the capital, Warsaw, to honour the late president Lech Kaczynski, who died. They walked in single file, guarded by police wearing surgical masks.

The crash in thick fog near Smolensk in western Russia was Poland’s worst air disaster since the second world war and stunned the country. It also deepened political divisions and revived suspicions about Russia, Warsaw’s former cold war master.

President Andrzej Duda, an ally of the ruling Law and Justice party (PiS), which was founded by Kaczynski and his twin brother Jaroslaw, expressed regret that the coronavirus outbreak in Poland made it impossible to mark the tragedy properly.

Critics, including opposition politicians, accused PiS officials of flouting restrictions that limit public gatherings and have left many cemeteries in the country closed to the public.

“This is not all right. With all certainty there was a way to mark today’s anniversary by following the rules that all Poles must follow, and that Poles pay fines for breaking,” said Jan Grabiec, spokesman for the centrist opposition party Civic Platform (PO).

Many Poles, including Duda, suspect that the crash was not caused by pilot error, as an official investigation by Poland’s previous centrist government concluded, but by foul play.

“After 10 years, it’s difficult to say anything or predict whether the case can ever be resolved,” Duda said in Krakow after visiting Kaczynski’s grave in a crypt in Wawel Cathedral.

“We don’t have basic evidence, the wreckage is still in Russia, the black boxes are still in Russia.“

Poland’s foreign ministry said in a statement that it had renewed demands that Moscow return the wreckage of the ageing Tupolev aircraft. “There are no provisions in international law that allow Russia to withhold Polish property,” it said.

Russian authorities said on Friday there was no evidence of an explosion on board the plane, as some in Poland allege.

Russia’s Investigative Committee said in a statement that crew errors led to the accident.