MOSCOW — A plane carrying the Polish president, Lech Kaczynski, his wife and other high-ranking officials crashed in a heavy fog in western Russia on Saturday morning, killing all aboard, Polish officials said.

Russian television showed chunks of still-flaming fuselage scattered in a bare forest near Smolensk, where the president was arriving for a ceremony commemorating the murder of more than 20,000 Polish officers by the Red Army as it invaded Poland.

The governor of Smolensk region, Sergei Antufiyev, said early reports suggested that the plane, landing in a thick fog, did not reach the runway but instead hit the treetops and fell apart. Russian President Dmitri A. Medvedev ordered top officials to rush to the scene and opened an investigation into the causes of the crash.