The Polish and Russian governments should assume full responsibility for the Smolensk air disaster and Prime Minister Donald Tusk should resign, Law and Justice leader Jaroslaw Kaczynski said on Thursday.

Polish experts in Moscow probing the plane crash that killed the Polish president and 95 others near Smolensk in April said on Wednesday they were "dissatisfied" with the documents supplied by Russia.

In an interview with Polish Radio, Kaczynski criticized the Polish government for being "ineffective and weak" with Russia over the investigation into the death of his twin brother, President Lech Kaczynski.

"The Russian or Polish governments...should take moral responsibility for the Smolensk air disaster," he said.

"The government should have turned [the investigation] into an international issue. Instead, it does not do anything and pretends that relations between Poland and Russia are continuing to improve," Kaczynski said.

It will be difficult to establish the truth about the causes of the April 10 air crash, he added.

"The Polish Prosecutor's Office has to rely on what it receives from Russian investigators," Kaczynski said.

The Polish Tu-154 pilots cannot be blamed for the crash, he went on.

"The pilots must have been misled. I absolutely disagree with the idea that someone put pressure on them. I knew my brother and he would not have given an order to land if it was dangerous," Kaczynski said.

The Tu-154 crashed while carrying Lech Kaczynski and other senior Polish officials to a commemoration ceremony for the 1940 Katyn massacre of more than 20,000 Poles by Soviet forces near Smolensk.

MOSCOW, September 23 (RIA Novosti)