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TEHRAN — Twenty American activists, writers and commentators flew to Iran this week to participate in a two-week conference on U.S. police brutality and racism.

Political scientist and commentator Wilmer Leon said he welcomed the opportunity to appear at the Third International Conference of Independent Thinkers and Scholars.

"The United States holds itself out as being the bastion of human rights, the arbiter of human rights, the shining city on the hill as President [Ronald] Reagan tried to characterize it," Wilmer told NBC News at the conference center in Tehran earlier this week. "And there are incredible contradictions between what America is supposed to stand for and the practices and atrocities that America continues to engage in."

The deaths of unarmed black men have sparked widespread outrage, with the shootings of 17-year-old Trayvon Martin in 2012 in Florida and 18-year-old Michael Brown in 2014 in Ferguson, Missouri, among those inspiring protests under the "Black Lives Matter" moniker.

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Iranian organizers told NBC News that they had paid for attendees' expenses in the country, but it did not say whether their flights were paid for. Organizers said the Americans would be speaking to university students and appearing on talks shows.

At a keynote speech, Ahmad Salek, a cleric and head of the cultural committee in Iran's parliament, referred to the U.S. as the "Great Satan" — a common refrain among Iranian hardliners — and compared its police and law enforcement to ISIS. He also vowed that "Israel will not exist in 25 years — Muslims of the world must come together to ensure this."

Last year's Horizon conference was accused of being anti-Semitic after the program included a panel discussion entitled "Zionist Fingerprints on the 9/11 Cover-up." It was also condemned by the Anti-Defamation League, a prominent Jewish advocacy group.

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When asked by how he felt about comparisons between the U.S. and ISIS, poet and Harvard University fellow Amir Sulaiman said "the scale" of murders was not the same.

"But I do understand the ideological reference ... of you killing an innocent person an unarmed person and the state allowing it," he said.

One of the conference's organizers, U.S.-educated filmmaker Nader Talebzadeh, said victims of American police brutality had been invited to attend, but "a lot of them did not have passports" and could not come.

Iran is no stranger to controversial conferences. In 2006, an international group participated in the International Conference to Review the Global Vision of the Holocaust in Tehran. It was widely condemned as a gathering of Holocaust deniers.