A longstanding adviser to Viktor Orbán has resigned in protest at “a pure Nazi speech” the Hungarian prime minister gave that was “worthy of Goebbels”. Zsuzsa Hegedüs, one of Orbán’s longest-serving advisers, has known the prime minister since 2002 and described her relations with him as friendly. However, in her resignation letter – published by the Hungarian news outlet hvg.hu on Tuesday – she said she had become increasingly uncomfortable with Orbán’s “illiberal turn” in recent years. Orbán has made anti-migration rhetoric a key part of his political platform since 2015, and frequently uses far-right language, but his speech on Saturday – in which he spoke out against “race mixing” – was extreme even by his standards. In the speech, Orbán said mixing between Europeans was acceptable, but Europeans mixing with non-Europeans created “mixed race” people. “We are willing to mix with one another, but we do not want to become peoples of mixed race,” said Orbán. He added that countries where this was seen as acceptable are “no longer nations”. Hegedüs said she had long defended the prime minister against accusations of antisemitism, but believed his latest speech to be indefensible. “I sincerely regret that such a disgraceful stance has forced me to sever our relationship,” she wrote. Orbán’s office published his reply to Hegedüs in which he accepted her resignation, but denied he was racist. “You can’t be serious about accusing me of racism after 20 years of working together. You know better than anyone that in Hungary my government follows a zero-tolerance policy on both antisemitism and racism,” he wrote. Orbán’s speech, given at an event in Băile Tuşnad, Romania, where he traditionally makes an annual keynote address, prompted an immediate backlash inside Hungary and abroad. Such criticism is nothing new, and Orbán thrives on his portrayal as a fighter against so-called political correctness and European liberal elites. However, resignations on matters of principle from his inner circle are extremely rare, and show that even among some parts of the right there is unease at how his rhetoric on race is developing. Next week Orbán is due to travel to Dallas, where he will open CPAC Texas, a gathering of US conservatives. Orbán counts the former US president Donald Trump among his many admirers on the American right.