Jaroslaw Kaczynski, the twin brother of the late Polish president who died in a plane crash, said on Saturday the causes of the disaster had yet to be established.
The Soviet-built Tu-154 aircraft crashed on April 10 near the western Russian city of Smolensk when it attempted to land in thick fog, killing all 96 people on board, including President Lech Kaczynski, his wife and other top state officials.
In an interview with public television TVP1, Jaroslaw Kaczynski said the investigation into the crash should be transferred from Russia to Poland.
"It would be a test of credibility for both sides," he said, according to the Polish Radio External Service.
"We have small knowledge of the causes of the disaster."
A Russian lawmaker said on Friday Poland was "content with Russia's investigation into the crash."
Konstantin Kosachyov, who heads the international affairs committee at the lower house of the Russian parliament, said after a meeting with Polish Foreign Minister Radoslaw Sikorski that the minister had "never heard of any complaints against the Russian side and the way the investigation is being conducted."
Russian and Polish investigators and experts are jointly investigating the causes of the crash. Polish military prosecutors are also conducting their own separate investigation.
An Interstate Aviation Committee spokeswoman said on Friday Russia will hand over to Poland the flight data recorders from the Polish presidential plane on Monday.
MOSCOW, May 29 (RIA Novosti)