The U.S. government apologized for using the phrase “Polish death camp” instead of “Nazi death camp” while awarding a posthumous Presidential Medal of Freedom in honor of Jan Karski, a Polish resistance leader, who relayed the horrors of the holocaust to the western allies at the end of World War II.

During the ceremony, President Barack Obama said: Jan served as a courier for the Polish resistance during the darkest days of World War II. Before one trip across enemy lines, resistance fighters told him that Jews were being murdered on a massive scale, and smuggled him into the Warsaw Ghetto and a Polish death camp to see for himself. Jan took that information to President Franklin Roosevelt, giving one of the first accounts of the Holocaust and imploring to the world to take action.

The verbal gaffe has sparked outrage across Poland, which has long claimed that as a victim of German Nazi aggression itself, the Poles cannot be held responsible for the death camps the Nazis built on Polish soil, like Auschwitz-Birkenau and Treblinka.

About 6 million Poles died during World War II, more than half of them Jews. Prior to the war, Poland had 3.5 million Jews, or about 10 percent of the total population, one of the largest such communities in Europe. By the end of the war, 90 percent of Polish Jews had been killed.

The president misspoke, said National Security Council spokesman Tommy Vietor. He was referring to Nazi death camps in Poland. We regret this misstatement, which should not detract from the clear intention to honor Mr. Karski and those brave citizens who stood on the side of human dignity in the face of tyranny.

However, Polish officials are demanding a direct apology from Obama himself.

Radoslaw Sikorski, the Polish foreign minister, wrote on his Twitter account: The White House will apologize for the outrageous mistake. It's a pity that ignorance and incompetence overshadowed such a momentous ceremony.

Poland’s President Donald Tusk has also demanded an apology, or at least an explanation, from Washington on the matter.

I am convinced that today our American friends are capable of a stronger reaction ... than just the correction itself and the regret which we heard from the White House spokesperson, Tusk said in a statement.

The subject is extremely sensitive for the Poles – while Poland has had a long history of anti-Semitism, there were a significant number of Polish “righteous gentiles,” that is, Christians who risked their lives to save the Jews. Indeed, the Yad Vashem in Israel has identified more than 6,000 Polish Christians who saved Jewish lives during the holocaust, more than any other nation.

Ironically, Obama visited the Warsaw Ghetto memorial last year and has frequently praised the bravery of Polish resistance fighters.

Karski died in 2000 at the age of 86.