Hungary has summoned the top US diplomat in Budapest after Senator John McCain described Prime Minister Viktor Orban as a "neo-fascist dictator".
The Hungarian government rejected the remarks, which it said were totally unacceptable.
Sen McCain was speaking in the US Senate on Tuesday before a vote on the appointment of a former TV soap opera producer as ambassador to Hungary.
Colleen Bell was "totally unqualified" for such a role, Sen McCain said.
The Republican senator had been unimpressed with Ms Bell this year when he questioned her during her confirmation hearing about what she planned to do differently from her predecessor as ambassador to Budapest.
She was widely seen as giving a faltering performance.
The former The Bold and The Beautiful producer, he said on Tuesday, was a political appointee who had contributed $800,000 (£510,000; €650,000) to President Barack Obama's last election campaign.
However, it was his next comments that most riled the Hungarian government and prompted Foreign Minister Peter Szijjarto to summon US charge d'affaires Andre Goodfriend.
"I am not against political appointees," the senator said. "I understand how the game is played, but here we are, a nation (Hungary) on the verge of ceding its sovereignty to a neo-fascist dictator, getting in bed with (Russian President) Vladimir Putin, and we're going to send the producer of The Bold and The Beautiful as our ambassador."
Mr Orban has in recent months adopted closer relations with Russia, opposing EU and US sanctions imposed on key officials in Moscow because of the conflict in Ukraine. He has also advocated turning Hungary into an "illiberal democracy".
The foreign ministry state secretary in Budapest said Hungary rejected Sen McCain's remarks, both about Mr Orban and relations with the government in Moscow.
Mr Szijjarto added that voters had three times backed the ruling Fidesz party's vision of "how they imagine the future of the country".
Thousands of Hungarians took to the streets in October to protest against the government's proposed tax on internet data usage, ultimately forcing ministers to shelve the plans.