OSWIECIM, Poland — Under thin sunshine, Vice President Pence stood silently before a specially reinforced wall against which German Nazis executed some of the estimated 1.1 million people slaughtered at Auschwitz.

The long moment of reflection Friday was part of a somber walking tour of the world’s most infamous former Nazi death camp and the remnants of a satellite camp, Birkenau, that are now a Polish state museum.

Shortly before, Pence and his wife, Karen Pence, had walked through the iconic Auschwitz camp gate, under crude metal letters spelling out the cruelly ironic Nazi motto “Arbeit Macht Frei,” or “Work Makes You Free.”

His visit was the emotional heart of a four-day European diplomatic trip focused on what the Trump administration calls Iran’s threatening posture and support for terrorism, and on spotlighting White House support for Israel.

Pence met with Israeli Prime Minister Benjamin Netanyahu on the sidelines of a U.S.-planned Middle East conference in Poland on Thursday, and the two men toured a memorial to Warsaw’s murdered Jews.

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Speaking with reporters after leaving the camp Friday, Pence likened the Nazi genocide to the vow of modern-day Iran to “wipe Israel off of the map of the Middle East” and said that Tehran voices “the same vile, anti-Semitic hatred that animated the Nazis in Europe.”

“And the lesson of the 20th century is that when authoritarian leaders breathe out anti-Semitic threats of violence against the Jewish people, freedom-loving people should take them seriously and be prepared to confront them,” Pence said.

Pence defended President Trump’s response to a deadly white-supremacist march in Charlottesville in 2017. Despite marchers chanting “Jews will not replace us,” Trump said there were “fine people on both sides” of a clash that killed a counterprotester.

“There is no tolerance in our administration for white supremacists or anti-Semitism,” Pence said Friday.

“I think the president was very clear in his condemnation of the Nazis and the white supremacists at Charlottesville, and I know he feels very strongly about that,” Pence said.

As a candidate, Trump drew criticism for a 2015 remark to the Republican Jewish Coalition that some construed as repeating anti-Semitic tropes about Jewish wealth and influence.

As president, he retweeted a doctored video mocking his 2016 Democratic rival, Hillary Clinton, from an account that had previously posted racist and anti-Semitic material.

Trump’s equivocal relationship with white nationalism and its echo of Nazism coexists with strong backing for Israel and political support from conservative, pro-Israel Jews. Trump fulfilled a campaign promise to declare contested Jerusalem the capital of Israel and move the U.S. Embassy there, leading to a boycott of his administration by the Palestinian Authority.

Trump and Pence have condemned a tweet from freshman congresswoman Ilhan Omar (D-Minn.) that many construed as an anti-Semitic suggestion that U.S. support for Israel is motivated by money.

Omar, who has apologized for the tweet, rejected Trump’s call that she resign, saying in a tweet Wednesday directed at the president: “You trafficked in hate your whole life—against Jews, Muslims, Indigenous, immigrants, black people and more.”

Omar has been critical of Israel for its occupation of the West Bank and treatment of Palestinians.

Trump son-in-law and adviser Jared Kushner, who is accompanying Pence in Europe, aired rough ideas about the Trump administration’s Middle East peace plan with diplomats attending the conference in Poland. The administration has kept details of the package secret ahead of an expected release after the Israeli national elections in April.

Pence, a Christian, prayed privately near the remnants of a crematorium at Birkenau and appeared deeply moved as he signed a memorial book. He spent some three hours at the sites and said later he was still struggling to absorb the enormity of what happened there.

Asked whether he would recommend that Trump also visit, Pence did not answer directly.

“I think it’s important for everyone to see it,” Pence said, “everyone who loves freedom to see it.”