A speech by Hungary's prime minister on migration has been described as unacceptable even by the standards of "the most bloodthirsty racist" by one of his advisers.
During his address, Viktor Orban said countries with large-scale migration from outside Europe "are no longer nations".
His colleague Zsuzsa Hegedus condemned the remarks, comparing them to the kind of language used in Nazi Germany.
Her response stands as a rare reprimand from within the governing ranks of Hungary's leader, who has long been accused by the European Union of eroding democratic institutions and norms.
In a resignation letter, Ms Hegedus, who has worked with Mr Orban for the past 20 years, said: "I am sincerely sorry that I have to end a relationship due to such a shameful position.
"I was left with no other choice."
She told the leader that his comments were unacceptable even by the standards of "the most bloodthirsty racist" and said he was presenting "a pure Nazi text worthy of Goebbels", referring to Joseph Goebbels, the chief Nazi propagandist under Adolf Hitler.
In his speech, which he made last Saturday, Mr Orban said: "There is a world in which European peoples are mixed together with those arriving from outside Europe," he said in Baile Tusnad, a majority ethnic Hungarian city in Romania.
"Now, that is a mixed-race world."
In what he described as "our world", Mr Orban said "people from within Europe mix with one another".
"This is why we have always fought: we are willing to mix with one another, but we do not want to become peoples of mixed-race," Mr Orban said.
He went on to say that the migration has "split the West in two" with one half becoming "a world where European and non-European peoples live together."
"These countries are no longer nations: they are nothing more than a conglomeration of peoples," he remarked.
Mr Orban is known for his anti-migration comments but criticism from within his closest circle has been very rare.
'You can't be serious about accusing me of racism'
Ms Hegedus also sent a copy of her resignation letter to Hungary's chief rabbi, Robert Frolich, who also criticised Mr Orban's remarks, according to Hungarian media.
Mr Orban accepted Ms Hegedus' resignation but dismissed her criticism.
"You can't be serious about accusing me of racism after 20 years of working together," he wrote in a letter to her.
"You know best that my government follows a policy of zero tolerance when it comes to antisemitism and racism in Hungary."
Mr Orban will travel to the US next week to address a gathering of conservative activists, to whom he has been a hero to many for his push against immigration and LGBTQ rights.