Polish Prime Minister Jaroslaw Kaczynski said Thursday that a new exhibition in Berlin on Germans expelled from Eastern Europe after World War II was "very bad, very disturbing and very sad."

The "Forced Paths" exhibition, which opened Thursday, was initiated by Erika Steinbach, a conservative lawmaker and the head of Germany's Federation of Expellees, a group that represents and remembers the estimated 12.5 million Germans expelled from their homes as a result of the war.

The exhibit is an irritant in relations between Germany and Poland, which suffered under a brutal occupation by the Nazis in World War II. Many Poles fear the exhibit will present a one-sided account of wartime suffering and create an impression that the Germans were mostly victims — rather than perpetrators — of the war.

"I think we are dealing with a very bad, very disturbing and a very sad event," Kaczynski told reporters during a visit to the site of the former Nazi death camp of Stutthof, located on the Baltic coast near Gdansk.

"We would like everything that is linked to the name of Ms. Erika Steinbach to end as soon as possible because nothing good is going to emerge from it for Poland, for Germany, for Europe."

The memory of "who was the aggressor and who was the victim" must be clearly preserved, he added.

During the war, Poland lost some 6 million citizens — half of them Jews. About 2 million Poles were also displaced when the Third Reich collapsed and borders were moved westward.

Steinbach hopes the exhibition will be the first step toward a permanent center documenting the plight of expellees, chiefly Germans but also other groups. Many of the expelled Germans came from what is now Poland.

Tensions over the legacy of World War II flared between both nations two years ago after a small group of Germans calling itself the Prussian Claims Society threatened court action to reclaim ancestral property in present-day Poland.

It hasn't made good on that threat so far, but the idea prompted Poland's parliament to urge the government to seek reparations from Germany for losses suffered during the Nazi occupation.

The government refused, but some city authorities have drawn up estimates of material losses, including some $54 billion of estimated damage in Warsaw alone. The estimate was made under then-Mayor Lech Kaczynski, Jaroslaw Kaczynski's twin brother and now president of Poland.

Germany's government opposes restitution claims by Germans against Poland and the group has little public support.