Poland's government has accused European Council president Donald Tusk of betraying national interests and bowing to Moscow in the investigation of the 2010 plane crash in Russia that killed Polish President Lech Kaczynski and 95 others.
Poland's ruling conservative party is led by the late president's twin, Jaroslaw Kaczynski, a political foe who accuses Mr Tusk of contributing to his brother's death.
Mr Tusk was Poland's prime minister in 2010.
The accusations are the latest development in the Law and Justice party's efforts to undermine Mr Tusk's image in Poland.
Defence minister Antoni Macierewicz, who heads a special commission reinvestigating the crash, has notified the military section of the National Prosecutor's Office that he suspects Mr Tusk committed a crime against Poland when he failed to secure Poland's participation in the investigation of the crash near Smolensk, Russia, or the return - to this day - of the wreckage and of the plane's flight recorders.
"Prime Minister Donald Tusk struck an illegal agreement with Vladimir Putin to Poland's detriment and should face criminal responsibility for that," Mr Macierewicz told the Gazeta Polska Daily newspaper.
Government spokesman Rafal Bochenek said that Mr Tusk's decision "prevented full investigation of the circumstances" of the crash.
Mr Tusk, in Brussels, said the matter was hard to comment on.
"This is not a matter of legal or political nature, it is purely about emotions and obsessions," he said in comments forwarded by his spokesman.
"Therefore, it is not within my competence to comment on cases like this one."
Independent investigations by aviation experts in Poland and in Russia concluded that mistakes by insufficiently trained crew coupled with poor visibility at the rudimentary military airport led to the crash, which was the worst accident for Poland's state since the Second World War.
A criminal investigation seeking those responsible is still under way in Poland.
Mr Macierewicz is heading a probe by aviation experts and forensics looking for proof to support his and Mr Kaczynski's view that the crash was an attack on the Polish delegation.
They have not yet presented their conclusions.
President Kaczynski was leading a delegation going to an anniversary memorial for some 22,000 Polish officers - prisoners of war - killed by the Soviet secret police in 1940 during the Second World War.