MOSCOW - The twin brother of former Polish President Lech Kaczynski believes the 2010 plane crash that killed his brother was an assassination and he wants the European Union to investigate.

Jaroslaw Kaczynski said that explosions might have brought down the plane, which crashed while trying to land amid heavy fog near Smolensk, Russia, April 10, 2010. The crash killed the president, his wife and nearly 100 other top Polish officials who were en route to a ceremony in Russia commemorating the massacre of an estimated 22,000 Polish military officers in 1940 by the Soviet secret police.

"If there were explosions [on board], if this catastrophe looks increasingly like an assassination, then this means there is a new quality to international politics," Kaczynski said Wednesday, according to the Associated Press.

Jaroslaw Kaczynski is the leader of Poland's nationalist Justice and Law Party, which has opposed the government's efforts to improve relations with Russia. His comments would appear to point a finger at Russia, which many Poles view suspiciously ever since the days when the Soviet Union controlled Poland. President Kaczynski had been a vocal critic of Moscow, which some people have suggested would be a possible motive for any assassination.

Conspiracy theories have echoed since the deadly crash took place, and this is not the first time the late president's brother has expressed concerns about the circumstances of the accident aboard the Russian-built plane. But his comments this week are the most direct accusation that foul play was the deliberate cause of his brother's death.

Polish and Russian investigations into the crash concluded that fog and pilot error were to blame for the crash, as well as pressure in the cockpit, which some believe suggests the pilot was urged to land despite poor weather conditions. Russian air traffic controllers had warned the pilot not to land. The Polish report blamed the Russian controllers for confusing instructions, although Russia has denied the allegation.

Jaroslaw Kaczynski lamented that the Polish public is beginning to forget about his brother's death. President Kaczynski's daughter, Marta, also appealed for an international investigation. Poland's Prime Minister Donald Tusk, however, has rejected the assassination theories.

The Associated Press contributed to this report.