Polish PM Jaroslaw Kaczynski has condemned an exhibition documenting the stories of millions of Germans expelled from Eastern Europe after World War II.
Mr Kaczynski said the exhibition aimed to distort history
Mr Kaczynski said the Berlin exhibition was "very bad, very disturbing".
The event is being staged by Germany's Federation of the Expelled, which plans to create a permanent exhibition centre in Germany.
The federation has been criticised by many people in Poland for portraying Germans as victims of the war.
"I think we are dealing with a very bad, very disturbing and a very sad event," Mr Kaczynski told reporters during a visit to the site of the former Nazi death camp at Stutthof - Sztutowo in Polish - in northern Poland.
"It's important to remember who were the murderers and who were the victims," he said.
Ms Steinbach highlights the plight of some 13 million expelled Germans
Mr Kaczynski also criticised Erika Steinbach, president of the Federation of the Expelled, who organised the exhibition.
"We would like everything that is linked to the name of Erika Steinbach to end as quickly as possible because nothing good will come out of it for Poland, Germany or Europe," he said.
Ms Steinbach said she hoped the exhibition would be the first step toward a permanent centre documenting the plight of the expelled people - mostly Germans but also other nations.
Critics say the exhibition is meant primarily to publicise the fate of the expelled Germans and that it runs the risk of minimising the Nazis' role in genocide and ethnic oppression, the BBC's Europe analyst Jan Repa says.
Supporters argue that it highlights a subject that needs open debate and that it covers the fate of non-Germans as well, he says.
The idea of a permanent memorial was opposed by Germany's Social Democrat government.
The present Christian Democrat-led administration of Chancellor Angela Merkel says it is keeping an open mind.
Both parties say they will not support claims for compensation by former expellees or their relatives - which would only exacerbate Germany's relations with its eastern neighbours, especially Poland and the Czech Republic.