President Barack Obama has written a letter to Polish President Bronisław Komorowski expressing “regret” for saying “Polish death camp” while referring to Nazi concentration camps during a ceremony on Tuesday, the Associated Press reports.

Warsaw has been waging a campaign for years against phrases such as “Polish death camps” or “Polish concentration camps” to refer to Auschwitz, Treblinka and other Nazi killing sites. The language deeply offends Polish sensitivities because Poles not only had no role in running the camps, but were considered racially inferior by the Germans and were themselves murdered in them in huge numbers.

President Obama Writes Polish President to Express Regret for Death Camp Remark“I inadvertently used a phrase that caused many Poles anguish over the years and that Poland has rightly campaigned to eliminate from public discourse around the world,” Obama said in the letter released by Polish President Bronisław Komorowski’s office.

(Related: Why is the Polish PM Demanding an Apology From President Obama?)

“The events of the past few days and the U.S. president’s reply may, in my opinion, mark a very important moment in the struggle for historical truth,” President Bronislaw Komorowski told reporters.

In case you missed it, here is the president’s “death camp” remark (via C-SPAN):

President Obama falsely identified Nazi death camps as Polish during a ceremony that posthumously awarded the Medal of Freedom to Jan Karski, a resistance fighter who struggled to tell the outside world about the murder of Jews in his country.

Karski, who was Catholic, smuggled himself into the Warsaw Ghetto and a death camp, witnessing the atrocities committed against the Jews firsthand. He then took that information to President Franklin Delano Roosevelt and other Allied leaders, imploring the world to act.

Karski later became a professor at Georgetown University and died in 2000.

President Komorowski said Wednesday that he knew Obama’s words did not reflect any bad intentions but that they were nonetheless “unjust and painful.” He wrote that day to Obama, and Obama’s letter came in reply to that.

In his response, Obama noted that “the Polish people suffered terribly under the brutal Nazi occupation during World War II.”

“In pursuit of their goals of destroying the Polish nation and Polish culture and exterminating European Jewry, the Nazis killed some six million Polish citizens, including three million Polish Jews during the Holocaust,” Obama wrote. “The bravery of Poles in the underground resistance is one of history’s great stories of heroism and courage.”

Later Friday, Polish Foreign Minister Radek Sikorski tweeted in reaction to Obama’s letter: “Thank you, President Obama. Truth, honor and the legacy of Karski satisfied. Please feel free to send us your staffers for re-education.”

“The issue itself is not over,” Poland’s Prime Minister Donald Tusk said at a press conference in Bucharest. “Let us put this incident behind us, but we will not rest until we will make sure such a situation never happens again.”

Here is the full text of the president’s letter to President Komorowski:

Thank you for your letter of May 30. I was proud to honor Jan Karski with the Medal of Freedom, our nations’s highest civilian honor. My decision to do so was a reflection of the high esteem in which the American people hold not only a great Polish patriot, but the extraordinary sacrifices of the Polish people during the Nazi occupation of the Second World War.

In referring to “a Polish death camp” rather than ” a Nazi death camp in German-occupied Poland,” I inadvertently used the phrase that has caused many Poles anguish over the years and that Poland has rightly campaigned to eliminate from public discourse around the world. I regret the error and agree that this moment is an opportunity to ensure that this and future generations know the truth.

A we all know, the Polish people suffered terribly under the brutal Nazi occupation during World War II. In pursuit of their goals of destroying the Polish nation and Polish culture and exterminating European Jewry, the Nazis killed some six million Polish citizens, including three million Polish Jews during the Holocaust. The bravery of Poles in the underground resistance is one of history’s great stories of heroism and courage.

Moreover, there simply were no “Polish death camps.” The killing centers at Auschwitz-Birkenau, Belzec, Treblinka, and elsewhere in occupied Poland were built and operated by the Nazi regime. In contrast, many Poles risked their lives – and gave their lives – to save Jews from the Holocaust.

That is why I paid tribute to Polish victims of the Holocaust during my visit to the US Holocaust Memorial Museum in April. It is why I was honored to pay my respect at the Tomb of Unknown Soldier and the Monument to the Heroes of the Ghetto during my visit to Warsaw last year. An it is why, during the 65th anniversary of the liberation of Auschwitz-Birkenau in 201, I commended the government and people of Poland for preserving a place of such pain in order to promote remembrance and learning for the world.

I know well the bonds of friendship between our two countries. I was proud to welcome you to the NATO Summit in my home town of Chicago, which is home to the largest Polish community in the world outside Warsaw. As President, I have worked with you to strengthen the enduring ties between our nations so that our alliance is stronger than it has ever been.

Poland is one of America’s strongest and closest allies. We stand united in facing the challenges of the 21st century in Europe and around the world, and I am confident that, working together, we can ensure that the unbreakable bonds of friendship and solidarity between us will only grow stronger in the days and years ahead.

The Associated Press contributed to this report.