A spokesman for Prime Minister Viktor Orban confirmed he had received a letter from Clinton, but did not disclose its contents.
Orban’s centre-right party scored a landslide victory in a 2010 election. Orban’s government went on to pass measures critics say weaken institutions such as the Constitutional Court and meddle with press freedom.
The letter "put in writing the things she had articulated verbally before", spokesman Peter Szijjarto told the national news agency MTI on Tuesday. "The prime minister will, naturally, respond to the letter in due course."