Iran’s second annual New Horizons conference, an anti-American hate fest that U.S. lawmakers say highlights the country’s dangerous duplicity.

Among those in attendance at the conference—which the U.S. State Department admitted it was not even aware of—were notorious Holocaust deniers, American anti-Israel activists, and Iranian Supreme Leader Ayatollah Ali Khamenei’s closest adviser.

They were joined by two of Iran’s former nuclear negotiators, Saeed Jalili and Ali Asghar Soltanieh, both of whom were once responsible for inking a deal with the West over Tehran’s contested nuclear program.

The presence Jalili and Soltanieh triggered concern on Capitol Hill, where lawmakers warned that this is another sign that Tehran cannot be trusted to deal honestly in ongoing nuclear talks, which have been extended through November.

As the Obama administration continues to provide billions of dollars in sanctions relief to Tehran in a bid to foster a final nuclear deal, some in Congress say that the White House is letting itself be fooled into backing a bad deal with Iran.

“The so-called ‘New Horizon’ conference in Tehran proves why the current Iranian regime under President Hassan Rouhani is, at its core, no less extremist and dangerous than the regime under Mahmoud Ahmadinejad,” Sen. Mark Kirk (R., Ill.) said in a statement.

“The conference’s participants promoted anti-Americanism, anti-Semitism, and Holocaust denial,