This article was reported by Nicholas Kulish, Ellen Barry and Michal Piotrowski, and written by Ms. Barry.

WARSAW — A plane carrying the Polish president and dozens of the country’s top political and military leaders to the site of a Soviet massacre of Polish officers in World War II crashed in western Russia on Saturday, killing everyone on board.

President Lech Kaczynski’s plane tried to land in a thick fog, missing the runway and snagging treetops about half a mile from the airport in Smolensk, scattering chunks of fuselage across a bare forest.

The crash came as a stunning blow to Poland, wiping out a large portion of the country’s leadership in one fiery explosion. And in a chilling twist, it happened at the moment that Russia and Poland were beginning to come to terms with the killing of more than 20,000 members of Poland’s elite officer corps in the same place 70 years ago.