A report by Poland's opposition party says Russian aviation officials bear most responsibility for the crash last year of the Polish government plane in which the president was killed.
The Law and Justice party blamed the Russians for allowing the plane to land under almost no visibility and said the crew was provided with incorrect landing parameters.
Jaroslaw Kaczynski, the twin brother of the president who was killed in the crash, is the party head. The report is independent of two state probes into the crash.
President Lech Kaczynski and 95 others were killed in a plane crash in Russia on April 10, 2010. The official Russian report said the blame rested solely with the Polish pilot, whose decision it was to land.